Internal-combustion engines – Free piston – Single chamber; one piston
Reexamination Certificate
1999-02-22
2001-03-27
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Free piston
Single chamber; one piston
Reexamination Certificate
active
06205961
ABSTRACT:
TECHNICAL FIELD
The present invention relates to free piston internal combustion engines, and, more particularly, to piston and cylinder configurations within such engines.
BACKGROUND ART
Free piston internal combustion engines include one or more pistons which are reciprocally disposed within corresponding combustion cylinders. However, the pistons are not interconnected with each other through the use of a crankshaft. Rather, each piston is typically rigidly connected with a plunger rod which is used to provide some type of work output. For example, the plunger rod may be used to provide electrical power output by inducing an electrical current, or fluid power output such as pneumatic or hydraulic power output. In a free piston engine with a hydraulic output, the plunger is used to pump hydraulic fluid which can be used for a particular application. Typically, the housing which defines the combustion cylinder also defines a hydraulic cylinder in which the plunger is disposed and an intermediate compression cylinder between the combustion cylinder and the hydraulic cylinder. The combustion cylinder has the largest inside diameter; the compression cylinder has an inside diameter which is smaller than the combustion cylinder; and the hydraulic cylinder has an inside diameter which is still yet smaller than the compression cylinder. A compression head which is attached to and carried by the plunger at a location between the piston head and plunger head has an outside diameter which is just slightly smaller than the inside diameter of the compression cylinder. A high pressure hydraulic accumulator which is fluidly connected with the hydraulic cylinder is pressurized through the reciprocating movement of the plunger during operation of the free piston engine. An additional hydraulic accumulator is selectively interconnected with the area in the compression cylinder to exert a relatively high axial pressure against the compression head and thereby move the piston head toward the top dead center (TDC) position.
In a free piston internal combustion engine as described above, the plunger rod is slidingly carried by a pair of bearings/seals which are respectively disposed between the combustion cylinder and the compression cylinder, and the compression cylinder and the hydraulic cylinder. Each bearing/seal allows reciprocating movement of the plunger rod while at the same time sealing around the plunger rod to fluidly separate the associated adjacent cylinders. Since the plunger rod is slidingly carried by the pair of bearings/seals, the longitudinal axis of the plunger rod defines the axis of reciprocating movement of the piston. Because of manufacturing tolerances, etc., it is possible that the piston head may not be disposed exactly concentrically with the longitudinal axis of the plunger rod. Alternatively, it is possible that the longitudinal axis of the combustion cylinder may not be disposed exactly concentric with the longitudinal axis of the plunger rod carried by the pair of bearings/seals.
The present invention is directed to overcoming one or more of the problems as set forth above.
SUMMARY OF THE INVENTION
The present invention provides a free piston internal combustion engine with a piston having a piston head which acts as a bearing within the combustion cylinder to accommodate concentric misalignments between the piston head and plunger rod during use.
In one aspect of the invention, a free piston internal combustion engine includes a housing with a combustion cylinder and a second cylinder. A piston includes a piston head reciprocally disposed within the combustion cylinder, a second head reciprocally disposed within the second cylinder, and a plunger rod rigidly attached to each of and interconnecting the piston head and the second head. The piston head defines a bearing with the inside surface of the combustion cylinder. A single bearing is carried by the housing within the second cylinder and reciprocally carries the plunger rod. The single bearing is the only bearing which directly carries the plunger rod.
An advantage of the present invention is that the piston head and the single bearing carrying the plunger rod form the two bearing points of a sliding mass to accommodate concentric misalignments between the combustion cylinder and the hydraulic cylinder and/or concentric misalignments between the piston head and plunger rod.
Another advantage is that radial loading on the piston head and plunger rod associated with concentric misalignments are reduced or eliminated.
Yet another advantage is that the portion of the piston head defining the bearing surface is constructed from a material having low friction, low thermal expansion and high temperature resistance properties.
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patent: 5033427 (1991-07-01), Kawamura et al.
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patent: 1958416 (1971-05-01), None
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patent: 2214569 (1989-09-01), None
patent: WO 93/10342 (1993-05-01), None
Application Serial No. 09/082,135 filed May 20, 1998, entitled “Piston for Use in an Engine”.
TU Dresden—publication date unknown—earliest date 1993—Dresden University in Germany.
Bailey Brett M.
Berlinger Willibald G.
Benton Jason
Caterpillar Inc.
McMahon Marguerite
Taylor Todd T.
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