Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
2000-10-30
2003-01-07
Mah, Chuck Y. (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S482000, C277S584000, C277S589000
Reexamination Certificate
active
06502826
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a piston seal suitable for use in high pressure hydraulic cylinders commonly employed in work implements and the like.
BACKGROUND ART
Piston seals for high pressure hydraulic cylinders are typically mounted within a seal groove formed about the periphery of the piston of such hydraulic cylinders. Such high pressure piston seals include a rigid seal ring and an elastomeric energizer or load ring. The load ring is mounted in the seal groove under the seal ring and is compressed so as to provide a radial force on the seal ring to urge the seal ring into sealing engagement with the inner bore of the cylinder. Load rings typically have a round or elliptical cross-sectional configuration in a free (non-compressed) state, whereas the chamber in which the load ring is mounted is generally rectangular in cross-section. Thus, when the load ring is mounted in the chamber in the seal groove under the seal ring, voids are created in the corners of the seal groove where portions of the exterior surface of the load ring are exposed or are not contacting either one of the walls of the seal groove or the inner side of the seal ring, even when the load ring is in a compressed state. When in a compressed state, the load ring bulges into, but does not completely fill, such voids.
In some applications, such as lift cylinders for hydraulic excavators, other earth moving equipment and the like, the piston seal may be exposed to extremely high pressure for extended periods of time. In addition, air may be ingested into the hydraulic fluid by means typical to mobile hydraulics such as by pump cavitation, by foaming of reservoir oil and by air entrainment in the oil supply. As a consequence, such air may be impinged against the exposed surfaces of the load ring for long periods of time under high pressure. It has been found that because the exposed surfaces of the load ring are stretched and under tension, air can permeate into the load ring through minute cracks or pores in the skin surface of the load ring. Subsequent actuation of the hydraulic cylinder can cause the rapid release of the high pressure and of the air now entrapped inside the load ring. When this occurs, the entrapped air undergoes a rapid decompression, which can “blow out” fragments from the exposed surfaces of load ring. This process is called explosive decompression. Over time and after numerous repetitions of such events, the load ring deteriorates to an extent to cause the seal to fail.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
A seal for a hydraulic cylinder piston capable of generating and withstanding high fluid pressures. The seal includes a split rigid seal ring adapted for receipt within a seal groove and having an outer cylindrical sealing surface adapted for sealingly engaging an inner hydraulic cylinder wall of a hydraulic cylinder.
The seal also includes an elastomeric energizer ring disposed within the seal groove radially inboard of the rigid seal ring. The elastomeric energizer ring is adapted to generate a radial force on the rigid seal ring for urging the outer cylindrical sealing surface into sealing engagement with the inner hydraulic cylinder wall of the hydraulic cylinder. The energizer ring defines a pair of annular cavities at end junctures between the rigid seal ring and the elastomeric energizer ring. The elastomeric energizer ring also seals the inner diameter of the rigid seal ring and seal groove.
A pair of rigid wedge rings are shaped and fitted to substantially fill each respective annular cavity. When installed, both wedge rings are capable of creating a pressure differential between the pressure of said hydraulic cylinder and the elastomeric energizer ring sufficient to prevent significant gas infiltration into the elastomeric energizer ring and to prevent damage to the elastomeric energizer ring due to explosive decompression when the hydraulic cylinder is depressurized.
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Schroeder Jeffrey A.
Tennis Richard L.
Caterpillar Inc
Mah Chuck Y.
Pickard Alison K.
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