Seal assembly

Details Seal assembly Seal assembly

1999-07-26

2002-04-30

Knight, Anthony (Department: 3626)

Seal for a joint or juncture

Process of dynamic sealing

Piston ring for internal combustion engine

C277S435000, C277S446000, C277S460000, C277S472000

Reexamination Certificate

active

06378872

ABSTRACT:

FIELD OF THE INVENTION
This invention concerns seals and, more particularly, annular seals of a type for minimizing fluid leakage between reciprocally movable members.
BACKGROUND OF THE INVENTION
Various mechanical apparatus include first and second members, which are substantially coaxial and disposed for relative reciprocal movement. Exemplary are internal combustion engines, positive displacement pumps, pneumatic motors and other mechanical devices incorporating a piston and a cylinder assembly. Other examples will occur to the skilled artisan.
Commonly, the cylinder is defined by a bore having a cylindrical sidewall. The piston, a generally cylindrical member, includes a sidewall and a top. An end wall or head, opposing the top of the piston, closes one end of the bore. A chamber of variable capacity is defined within the bore between the head and the top of the piston. Pressurized fluid functions in this chamber. In an internal combustion engines, the fluid is the expanding gas of combustion which ignites and propels the piston downwardly or away from the head. Pressurized fluid from an external source is introduced into the chamber of a pneumatic motor to force movement of the piston. In a pump, which is companion to the engine and to the pneumatic motor, fluid is compressed and pressurized in the chamber.
To provide for relative movement between the members, the diameter of the piston must be less than the diameter of the bore. Frequently, substantial clearance is required. For example, it is well known that a piston is more sensitive to thermal expansion than is a cylinder. Accordingly, where heat is a factor, such as in internal combustion engine, additional space must be provided between the sidewall of the bore and the sidewall of the piston to accommodate thermal expansion of the piston. The space, commonly referred to as sidewall clearance, is generally in the range of fifteen ten-thousandths of an inch to five one-thousandths of an inch, or greater.
However, the piston must be sealed to the cylinder. Conventionally, this is accomplished by a device commonly referred to as a piston ring, an annular seal usually fabricated of metal such as cast iron. The ring is received within a mating annular ring groove formed into the sidewall of the piston. To facilitate expansion during installation, and for other reasons, the ring is radially severed.
The spacing between the opposed ends of the severed ring, known as the end gap, serves various functions after installation. Having an inherent tendency to expand, the ring maintains tension for attendant sealing against the sidewall of the cylinder as the bore increases in diameter as a result of wear. The end gap also allows for thermal expansion of the ring resulting from heat generated by friction, compression of fluid, combustion of fuel and other sources.
Although necessary and even beneficial, the end gap is also the source of considerable concern. Normal end gap clearance in a newly installed ring ranges from approximately ten one-thousandths of an inch to approximately forty one-thousandths of an inch. The end gap defines a path for leakage of fluids between the sidewall of the piston and the sidewall of the bore. Throughout the life of the device, the piston ring continuously expands as compensation for normal wear. As a result, the end gap ever increases with corresponding increase in leakage, usually referred to as a blow-by.
Efficiency, economy and service life of the apparatus is directly related to blow-by. In general, less than optimum output of the apparatus results from loss of pressure or compression of the fluid. Other deleterious effects are unique to the particular apparatus. In an internal combustion engine, for example, contaminating by-products of combustion suspended in the blow-by gases are carried into the lubricating system, which harms components throughout the engine.
In recognition of the desirability of enhancing the seal between the piston and the cylinder, the prior art has proposed various seals, which purportedly reduce or eliminate blow-by. Several prior art proposals are direct attempts to eliminate the end gap in the conventional piston ring. Various proposals include an insert, which spans the end gap and is received in a notch formed into the ring on either side of the end gap. Other proposals include the use of a relatively thin steel member, alternately named a ribbon member or a gap seal member, having a substantially rectangular cross-section. Also advanced is a plurality of severed annular members, installed in stacked arrangement with staggered end gaps. The prior art has also advocated the use of thin steel members, colloquially dubbed rails, in combination with ring members having a general resemblance to conventional piston rings. Being of substantially heavier construction than a rail and usually fabricated of malleable material, such as cast iron, the ring member is variously referred to as a packing member or a sealing ring. The ring member in combination with the rail member comprise a seal assembly of which various embodiments are known.
In accordance with one known arrangement, the rail resides within an annular groove formed into the inner circular wall of the seal member and exerts outwardly directed radial pressure to hold the seal member in contact with the sidewall of the bore. In another configuration, the rail occupies a space between the top of the seal member and the upper radial surface of the containing ring groove. Still other formations orient the radial axis of the rail at an angle.
For various reasons, annular seals of the foregoing character are not entirely satisfactory. For example, in an assembly wherein the rail resides within the seal member and exerts an expansive force, excessive friction is generated against the sidewall of the bore. Where only the rail contacts the sidewall, seating or breaking-in of the seal is substantially retarded or even prohibited. An angled rail is subject to vibration, commonly known as ring flutter, when used in connection with a rapidly reciprocating piston. A thin steel member exposed to extreme heat, such as when utilized as the top compression ring in an internal combustion engine, will become distorted.
Seal assemblies of the above character where devised mainly during the time period ranging from approximately the middle nineteen thirties to early nineteen fifties. During the early nineteen seventies, there was developed a seal assembly, which substantially remedied the foregoing deficiencies inherent in the prior art. Distributed by POWERFORMANCE INTERNATIONAL CORPORATION under the trademark TOTAL SEAL®, the seal assembly has achieved commercial success, especially for use in connection with four-stroke cycle internal combustion engines.
Briefly, the Total Seal® device, referred to as a ring set, includes a sealing ring member and a gap seal member. The sealing ring member, a severed annular member preferably fabricated of malleable metal such as cast iron, has thickness and radial dimensions to be received within a conventional piston ring groove in accordance with standard tolerances. Extending inwardly from the outer cylindrical surface along the underside of the sealing ring member is an annular recess in which is received the gap seal member. The intricacies and advantages of the ring are described in U.S. Pat. No. 3,811,690 and are well known to those having regard for the art.
Notwithstanding continuing success in the trade, the Total Seal® ring set has proven less than optimum for engines having circumferential intake and/or exhaust ports such as found in two-stroke cycle engines. As installed, the respective end gaps of the sealing ring member and of the gap seal member are diametrically opposed. The elastic expansiveness or outward radial force of a severed annular seal under tension is gradiently distributed throughout. Therefore, while the set as an assembly is free to move or work within the ring groove, theoretically, movement between the members should be prohibited as the result of the relative for

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