Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
1999-02-04
2001-09-04
Mah, Chuck Y. (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S448000, C277S460000, C029S888070
Reexamination Certificate
active
06283478
ABSTRACT:
The disclosure of Japanese Patent Application No. HEI 10-39226 filed on Feb. 20, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piston ring structural body for an internal combustion engine and, more particularly, relates to a piston ring structural body wherein an outer ring continuously formed of a resinous material without being provided with an abutment is pressed radially outwards by a ring tensile force applying member via an inner ring continuously formed of a resinous material without being provided with an abutment. The present invention also relates to a method of mounting the piston ring structural body.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. HEI 9-280373 discloses that a resinous piston ring continuously formed without being provided with an abutment is used to reduce the amount of blow-by gas (gas which leak to a crank case through a gap between a piston ring and a cylinder). In this publication, there is disclosed a piston ring structural body wherein an outer ring continuously formed of polytetrafluoroethylene (PTFE) as a fluororesin without being provided with an abutment is pressed radially outwards by a ring tensile force applying member composed of a metal coil expander via an inner ring also continuously formed of PTFE without being provided with an abutment.
In the piston ring structural body disclosed in the aforementioned publication, the ring is divided into the inner and outer rings. While the inner ring ensures sealability around a ring groove, the outer ring ensures sealability between a sliding portion thereof and a cylinder wall.
It is to be noted herein that the piston ring structural body disclosed in the aforementioned publication uses PTFE for both the inner and outer rings. However, PTFE has a low threshold value of PV (the product of a real pressure P and sliding speed V) and cannot provide the sliding portion that slides on the cylinder wall with sufficient durability. Furthermore, PTFE has a large coefficient of thermal expansion. Thus, when the temperature rises, the pressing force applied to the cylinder wall due to a tensile force of the coil expander becomes larger, which causes a problem of an increase in frictional loss of the engine.
SUMMARY OF THE INVENTION
In view of the aforementioned problem, it is an object of the present invention to enhance durability of a piston ring structural body of a type wherein an outer ring continuously formed of a resinous material without being provided with an abutment is pressed radially outwards by a ring tensile force applying member via an inner ring continuously formed of a resinous material without being provided with an abutment.
It is also an object of the present invention to provide a method of mounting such a piston ring structural body to a piston easily and reliably.
A first aspect of the present invention provides a piston ring structural body fitted into a ring groove of a piston. This piston ring structural body includes an outer ring continuously formed of a first resinous material without being provided with an abutment, an inner ring continuously formed of a second resinous material without being provided with an abutment, and a ring tensile force applying member for pressing the outer ring outwards in a radial direction of the piston via the inner ring. In this piston ring structural body, the first resinous material has a coefficient of thermal expansion and a breaking point that are lower than those of the second resinous material.
In the thus-constructed piston ring structural body, because the inner ring is more susceptible to deformation at a high temperature, the sealability around the ring groove is ensured and the coil expander can suitably apply a tensile force to the outer ring. The outer ring is unlikely to be deformed even at a high temperature, so that the outer ring smoothly slides on the cylinder wall surface without causing any damage to the sealability between itself and the cylinder wall surface.
In the first aspect of the present invention, the ring tensile force applying member may be a coil expander, which is a member composed of a metal wire wound like a coil.
Furthermore, in the first aspect of the present invention, the first resinous material may be polyimide and the second resinous material may be polytetrafluoroethylene.
In the thus-constructed piston ring structural body, the outer ring is made of polyimide and the inner ring is made of polytetrafluoroethylene (PTFE). Because the inner ring is more susceptible to deformation at a high temperature, the sealability around the ring groove is ensured and the coil expander can suitably apply a tensile force to the outer ring. The outer ring is unlikely to be deformed even at a high temperature, so that the outer ring smoothly slides on the cylinder wall surface without causing any damage to the sealability between itself and the cylinder wall surface.
Furthermore, in the first aspect of the present invention, at least a lower face of the outer ring may be coated with titanium nitride, chrome nitride or diamond-like carbon.
Thus, the lower face of the outer ring of the piston ring structural body, which has a construction wherein the outer ring continuously formed of polyimide without being provided with an abutment is pressed outwards in the radial direction of the piston by the coil expander via the inner ring continuously formed of PTFE without being provided with an abutment, is reinforced by being coated with titanium nitride (TiN), chrome nitride (CrN) or diamond-like carbon (DLC). Accordingly, the lower face of the outer ring is inhibited from being abraded despite contact with the ring groove, which occurs in accordance with the movement of the piston in the piston-axis direction.
In addition, the piston ring structural body according to the first aspect of the present invention can be used as a second ring fitted into a ring groove that is located at the second closest position to a top portion of the piston.
In addition, in the first aspect of the present invention, an outside sliding face of the outer ring that is in sliding contact with the cylinder wall may be divided in the top-to-bottom direction, and at least an upper edge of an uppermost sliding face may be provided with a chamfer.
Thus, the sliding face of the outer ring of the piston ring structural body, which has a construction wherein the outer ring continuously formed of polyimide without being provided with an abutment is pressed outwards in the radial direction of the piston by the coil expander via the inner ring continuously formed of PTFE without being provided with an abutment, slides on the cylinder wall and is divided in the top-to-bottom direction. Thereby, the entire cross-section of the outer ring is prevented from being displaced, and the outer ring is inhibited from changing its posture relative to the cylinder wall. Furthermore, the provision of the chamfer at the upper edge portion of the upper sliding face reduces the amount of oil raked upwards by the piston during an upward movement thereof and inhibits oil loss.
Furthermore, in the first aspect of the present invention, a contact portion of the inner ring that contacts the coil expander may be provided with an upper inclined face extending radially inwards and upwards and a lower inclined face extending radially inwards and downwards. Besides, angles of inclination of the upper and lower inclined faces with respect to a plane where the coil expander is disposed can be set within a range from 30° to 60°.
Thus, the piston ring structural body, which has a construction wherein the outer ring continuously formed of polyimide without being provided with an abutment is pressed outwards in the radial direction of the piston by the coil expander via the inner ring formed of PTFE without being provided with an abutment, ensures that the tensile force of the coil expander is suitably distrib
Kumai Teruo
Okamoto Michio
Mah Chuck Y.
Peavey Enoch E.
Pillsbury & Winthrop LLP
Toyota Jidosha & Kabushiki Kaisha
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