Expansible chamber devices – Piston – Welded – brazed or soldered
Reexamination Certificate
2000-02-28
2001-09-25
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Piston
Welded, brazed or soldered
C092S172000, C092S176000
Reexamination Certificate
active
06293185
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to hydraulic power units of the type which incorporate a cylinder block containing reciprocating pistons which, through pivotally attached slippers, are in operational engagement with a swashplate. Such hydraulic power units may operate as either pumps or motors. Specifically this invention is concerned with an improved piston for use in such hydraulic power units.
Typically, the pistons that are utilized in hydraulic power units of the aforementioned type have been manufactured from a metallic material, usually steel, which is heat treated. The particular material and heat treatment process utilized are selected to provide adequate structural strength and wear properties necessary for appropriate piston function and life. Closed end hollow pistons are shown in U.S. Pat. No. 3,319,575. Fluid conduits extending the length of the piston are shown in both the U.S. Pat. No. 3,319,575 and also in U.S. Pat. No. 3,882,762.
Because the piston interacts dynamically with both the cylinder block and the slipper-to-swashplate connection which present different loading and wear challenges to the piston, it has been determined that the material property requirements of the piston are not necessarily uniform throughout the entire structure of the piston. For this reason, it is advantageous to provide a piston which is made up of more than a single material so that various structural elements of the piston may possess different strength and wear properties in its final form.
Generally, it has been determined that the cylindrical body of the piston which is in reciprocating contact with the bore of the cylinder block requires strength and surface wear properties necessitating the use of hardened medium carbon steel. The end of the piston which is connected to a slipper through a spherical joint is subject to compressive rotary and pivotal motion and does not require the extreme strength and wear properties of the cylindrical body. The spherical end of the piston can provide satisfactory function and life when formed of low carbon steel which is not hardened. Additionally, it is often advantageous for the spherical end of the piston to remain malleable to crimping of the end to retain the slipper to the piston in an assembled condition.
Therefore, it is a principal objective of this invention to provide a piston which is comprised of more than a single material.
Further, it is an objective of this invention to form a piston from multiple parts, each part being of a different metallic material.
It is also an objective of this invention to produce a piston which includes a hardened cylindrical body and a malleable spherical end.
It is a further objective of this invention to provide a piston which incorporates a conduit traversing the body and the insert as a path to communicate pressurized fluid from the cylinder bore to the slipper and swashplate operative connection.
Additionally, it is an objective of this invention to assemble the piston to a slipper for subsequent reciprocal operation in the bore of a cylinder block and operative connection with a swashplate in a hydraulic power unit.
These and other objectives will be apparent to those skilled in the art.
SUMMARY OF THE INVENTION
A piston for a cylinder block of a hydraulic power unit has a cylindrical body and one end terminating in a spherical surface. The cylindrical body may take the form of either a solid cylinder or hollow cylindrical tube. The spherical surface may take the form of either an internal cavity or an external ball, and is integral to an insert which is made as a separate piece from the cylindrical body. The body and insert are joined together to produce a complete piston.
The body, either in its solid or hollow form is made from a medium or high carbon steel material. The material is suitable for hardening to provide high structural strength and surface wear properties. The cylindrical body is formed to include an internal seat at one end to accommodate the positioning and attachment of the insert.
The insert, either in its internal or external spherical form is made of low carbon steel material. The material is capable of being subjected to heat treatment operations and still remain malleable. The insert is in the form of a simple cap which can be joined to one end of the body. The insert may also alternatively be formed in an elongated shape which incorporates a circular disc extended from the spherical surface end by an adjoining tubular neck structure. This elongated insert is used in conjunction with the hollow body to form a piston with a closed internal cavity.
In all cases, the final piston incorporates a conduit which passes through the body and the insert. This passage is used to provide a path for pressurized fluid to flow from the pressurized cylinder bore in the cylinder block through the piston and the slipper to the operative connection with the swashplate.
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Landwehr Mark A.
Stoppek Robert J.
Ryznic John E.
Sauer-Danfoss Inc.
Zarley McKee Thomte Voorhees & Sease
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