Expansible chamber devices – With lubricating means – Piston has lubricant retaining or conducting means
Reexamination Certificate
1999-02-04
2001-03-27
Look, Edward K. (Department: 3745)
Expansible chamber devices
With lubricating means
Piston has lubricant retaining or conducting means
C092S194000, C092S212000, C277S438000, C277S440000
Reexamination Certificate
active
06205908
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-39242 filed on Feb. 20, 1998 including the specification, drawing 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 with a ring groove that has fitted thereinto a piston ring structural body wherein a ring continuously formed of resin without being provided with an abutment is pressed radially outwards by a coil expander composed of a metal wire wound like a coil.
2. Description of the Related Art
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), Japanese Patent Application Laid-Open No. HEI 9-280373 discloses a piston equipped with a piston ring continuously formed of resin without being provided with an abutment. This publication discloses 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.
If the piston ring is provided with an abutment, a small amount of combustion gas leaks out toward a crank case through the abutment. The leaking combustion gas blows down oil which has adhered to the ring groove of the piston and the cylinder wall toward the crank case, whereby the amount of oil consumption is reduced.
However, in the case of a ring made of resin without being provided with an abutment, the aforementioned blow-down effect cannot be obtained. As a result, the oil that has adhered to the ring groove of the piston and the cylinder wall is not returned toward the crank case, and the amount of oil consumption may increase.
SUMMARY OF THE INVENTION
In view of the aforementioned problem, it is an object of the present invention to inhibit, in the piston using a piston ring continuously formed of resin without being provided with an abutment, the amount of oil consumption from increasing due to a phenomenon wherein oil which has adhered to a ring groove of a piston and a cylinder wall is not returned toward a crank case.
A first aspect of the present invention provides a piston including a piston ring structural body, a ring groove and a land portion. The piston ring structural body includes a ring that is continuously formed of resin without being provided with an abutment and slides against a cylinder wall. The piston ring structural body is fitted into the ring groove. The land portion is formed on an outer circumference of the piston on a side of a crank case with respect to the ring groove and at least has a portion more contiguous to the cylinder wall than a bottom portion of the ring groove. In this piston, the land portion has formed therethrough an oil return port that allows communication between a cylinder-side face of the land portion and an inner space of the piston.
In the thus-constructed piston, a surplus of oil, which has reached the cylinder wall at a location on the side of the crank case with respect to the ring that is continuously formed of resin without being provided with an abutment and slides on the cylinder wall, is introduced into the piston through the oil return port formed through the land portion, which is located on the side of the crank case with respect to the ring groove.
In the first aspect of the present invention, the land portion may have an oil transportation mechanism that transports oil which has reached the land portion to the oil return port when the piston moves toward the crank case.
In the thus-constructed piston, a surplus of oil, which has reached the cylinder wall at a location on the side of the crank case with respect to the ring that is continuously formed of resin without being provided with an abutment and slides against the cylinder wall, is transported to the oil return port by the oil transportation mechanism of the land portion, which is located on the side of the crank case with respect to the ring groove. The oil is then introduced into the piston through the oil return port.
In the first aspect of the present invention, the oil transportation mechanism may have a first portion that is formed on the land portion and located nearest to the cylinder wall and a second portion that is formed on the side of the crank case with respect to the first portion of the land portion and located farther from the cylinder wall than the first portion is from the cylinder wall. In this case, the oil return port allows communication between the cylinder-side face of the second portion and the inner space of the piston.
In the thus-constructed piston, a surplus of oil, which has reached the cylinder wall at a location on the side of the crank case with respect to the ring that is continuously formed of resin without being provided with an abutment and slides on the cylinder wall, is raked downwards by the first portion formed on the land portion, which is located on the side of the crank case with respect to the ring groove. The oil is then transported to the oil return port and introduced into the piston therethrough.
In addition to the features of the first aspect of the present invention, the present invention may further be specified according to a second aspect thereof. That is, the aforementioned piston ring structural body is composed of an outer ring continuously formed of a resinous material without being provided with an abutment, an inner ring continuously formed of a resinous material without being provided with an abutment, and a metal coil expander for pressing the inner ring radially outwards.
In the thus-constructed piston, a surplus of oil, which has reached the cylinder wall at a location on the side of the crank case with respect to the outer ring continuously formed of a resinous material without being provided with an abutment, is introduced into the piston through the oil return port formed through the land portion, which is located on the side of the crank case with respect to the ring groove.
In the second aspect of the present invention, the outer ring may be made of polyimide and the inner ring may be made of polytetrafluoroethylene.
In addition to the features of the first aspect of the present invention, the present invention may further be specified according to a third aspect thereof. That is, the aforementioned piston ring structural body is composed of an outer ring continuously formed of a resinous material without being provided with an abutment, an inner ring made of a metal material and provided with an abutment, and a metal coil expander for pressing the inner ring radially outwards.
In the thus-constructed piston, a surplus of oil, which has reached the cylinder wall at a location on the side of the crank case with respect to the outer ring continuously formed of a resinous material without being provided with an abutment, is introduced into the piston through the oil return port formed through the land portion, which is located on the side of the crank case with respect to the ring groove.
In the third aspect of the present invention, the outer ring may be made of polyimide and the inner ring may be made of steel.
In the aforementioned aspects of the present invention, the outer ring may have a sliding face that slides along the cylinder wall, and an upper edge portion of the sliding face may be provided with a chamfer.
In the thus-constructed piston, even if oil has flown into the space above the outer ring, the oil is likely to return to the space below the outer ring during an upward movement of the piston.
REFERENCES:
patent: 3494262 (1970-02-01), Ho
Kumai Teruo
Okamoto Michio
Lazo Thomas E.
Look Edward K.
Pillsbury & Winthrop LLP
Toyota Jidosha & Kabushiki Kaisha
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