Internal-combustion engines – Particular piston and enclosing cylinder construction – Piston
Reexamination Certificate
2002-01-30
2004-01-13
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
Piston
Reexamination Certificate
active
06675761
ABSTRACT:
TECHNICAL FIELD
This invention relates to a piston and, more specifically, to a piston having a reinforcing ring band.
BACKGROUND
An internal combustion engine commonly includes a crankshaft and a plurality of cylinders, each cylinder having a piston, combustion chamber, glow plug or spark plug, and connecting rod. The piston and connecting rod are used to transmit power from the combustion chamber to the crankshaft. It is important for the interface of the combustion chamber and the piston to be sealed; this sealing is normally accomplished with a piston ring. The piston normally includes one or more piston rings which are each positioned by an annular ring groove.
The piston rings seal the combustion chamber between the piston and the cylinder wall. As the engine operates, combustion occurs and high temperatures are achieved in the combustion chamber. A portion of the heat from the combustion is absorbed in the piston and, for efficiency and longevity of the piston, must be channeled away from the piston by the rings to the walls of the combustion chamber.
Since aluminum conducts heat well, aluminum is used in manufacturing many pistons. However, since aluminum is very soft, as the piston travels in the cylinder, the piston rings tend to wear and disform the ring grooves, causing distortion of the ring groove configuration and exceeding design tolerances. This wear can result in a loss of sealing of the combustion chamber. This situation is exacerbated by the common practice of placing a twist or bias on the piston rings, which causes greater wear of the ring grooves.
It is thus common in the art to form the ring grooves in a ring band, of iron or another material having a higher wear characteristic than that of aluminum. The band is bonded to the piston during manufacture thereof. This ring band is intended to reinforce the piston such that the piston rings do not cause undue wear to the piston itself. Unfortunately, the material of the ring band often is a poorer conductor of heat than aluminum. Thus, the transfer of heat from the piston through the piston rings to the cylinder wall is impeded by this difference in conduction, resulting in less heat transfer than is desired.
U.S. Pat. No. 5,746,169, issued May 5, 1998 to Wolfgang Issler et al. (hereafter referenced as '169) discloses a piston including a ring band. '169 discloses several ring grooves, but only the topmost one of these grooves is formed in a reinforcing ring band. This is commonly done to try to balance the need for robust sealing of the combustion chamber with effective heat conduction. Each ring groove of '169 therefore has a disadvantage in either heat conduction or wear resistance. Should the piston rings of '169 be configured with a twist or bias to exert a greater force on one face of the ring grooves, wear on that face will be hastened, thus necessitating replacement of the piston.
The present invention is directed to overcoming one or more of the problems as set forth above.
SUMMARY OF THE INVENTION
In an embodiment of the present invention, a piston including a body portion, a ring band, and a ring groove is provided. The body portion is composed of a first material having a preestablished rate of thermal conductivity. The ring band is composed of a second material having a preestablished rate of thermal conductivity that is less than the rate of thermal conductivity of the first material. The ring groove has a top face and a bottom face. One of the top face and the bottom face is formed by the first material and the other of the top face and the bottom face is formed by the second material.
In an embodiment of the present invention, an engine is provided. The engine includes a combustion chamber, a connecting rod, a piston, and at least one ring groove. The piston is composed of a first material having a preestablished rate of thermal conductivity and a second material having a preestablished rate of thermal conductivity different from the rate of thermal conductivity of the first material. The piston is attached to the connecting rod. The ring groove is partially positioned in each of the first material and the second material.
In an embodiment of the present invention, a method of reinforcing a piston is provided. The piston has at least one annular groove having a top face and a bottom face. The method includes the steps of providing a piston of a first material, providing a band of a second material having a preestablished rate of thermal conductivity less than the rate of thermal conductivity of the first material, bonding the band to the piston, forming one of the top face and the bottom face in the first material, and forming the other of the top face and the bottom face in the second material.
In an embodiment of the present invention, a piston is provided. The piston includes a first material, a second material, at least one ring groove, and a piston ring. The ring groove is partially positioned in each of the first material and the second material. The piston ring is positioned in the ring groove.
In an embodiment of the present invention, a method of operating a reinforced piston is provided. The method includes the steps of providing a ring groove formed in the piston and having at least one wall portion comprised of each of a first material and a second material, providing a piston ring partially contained in the ring groove, moving the piston inside a cylinder in a reciprocating manner, and contacting the cylinder with the piston ring. The method also includes the steps of transferring heat from the piston to the piston ring to the cylinder via the first material, and resisting wear of the ring groove from the piston ring via the second material.
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Caterpillar Inc
Heming William B
McMahon Marguerite
Myers Liza B
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