Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
2002-02-06
2004-03-02
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S440000, C277S441000, C277S442000, C277S443000
Reexamination Certificate
active
06698763
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a stainless steel piston ring having excellent abrasion resistance.
BACKGROUND OF THE INVENTION
Conventional stainless steel piston rings of excellent abrasion resistance are of the type in which the piston rings have a nitride layer formed on the upper and lower surfaces and the inner and outer circumferential surfaces of the stainless steel base material of the piston rings, by applying the nitriding process to those surfaces, where the diffusion layer of the nitride layer on the outer circumferential surface is then exposed by removing the compound layer of the nitride layer on the outer circumferential surface, and, thereafter, the exposed diffusion layer has an ion-plating deposition layer of hard ceramic formed thereon by vacuum vapor depositing a hard ceramic thereon. This type of piston ring had a disadvantage in that, when cracks occur in the ion-plating deposition layer, the cracks would propagate to the nitride layer, thereby resulting in a degradation of the fatigue strength.
In order to overcome this disadvantage, a piston ring is proposed in the Japanese Patent Publication No. 3,090,520 in which the piston ring has only an ion-plating deposition layer formed directed on the outer circumferential surface of the stainless steel base material thereof, and where the nitride layer is only formed on the upper and lower surfaces and the inner circumferential surface of the stainless steel base material.
The ion-plating deposition layer formed directly on the stainless steel base material however has a problem in that it is inferior in adhesion to an ion-plating deposition layer formed on the diffusion layer, of a nitride layer on the stainless steel base material, exposed by removing the compound layer of the nitride layer. Furthermore, another problem exists in that, in case an ion-plating deposition layer is formed directly on the outer circumferential surface of the stainless steel base material, the stainless steel base material tends to slide directly in contact with the surface of a cylinder or cylinder liner, that is otherwise supposed to slide in contact with the surface of the ion-plating deposition layer, as the ion-plating deposition layer wears out, thereby causing scuffing or scuff-marks, where countermeasures against it of increasing the deposition layer thickness would cause degradation of the breakage resistance, and, at the same time, lead to an increase in the manufacturing costs.
The present invention has been made to solve these problems. Therefore, an object of the present invention is to provide a piston ring of the type in which a nitride layer is formed on the upper and lower surfaces and the inner and outer circumferential surfaces of the stainless steel base material of a piston ring, where an ion-plating deposition layer of hard ceramic is formed on the nitride layer of the outer circumferential surface, wherein the piston ring has an advantage in that degradation of the fatigue strength would not be caused, even when cracks occur in the ion-plating deposition layer.
The present inventors have come to think of, and devise, the principle of the present invention by recognizing that, although cracks cannot be prevented from occurring in the ion-plating deposition layer on the outer circumferential surface of a piston ring because the ion-plating deposition layer is lacking in toughness, degradation of the fatigue strength of the piston ring caused by such cracks could be prevented by restraining the propagation of cracks occurring in the ion-plating deposition layer at the upper and lower corner regions of the upper and lower surfaces and the outer circumferential surface, because the cracks mainly occur at these corners.
SUMMARY OF THE INVENTION
In order to accomplish the object described above, a piston ring is provided, according to a first embodiment of the present invention, that is an improved piston ring of the type that has a stainless steel base material having an upper surface, a lower surface, an inner circumferential surface and an outer circumferential surface, the surfaces each having a nitride layer formed thereon. The exposed diffusion layer has thereafter an ion-plating deposition layer of hard ceramic formed thereon by vacuum vapor deposition. The piston ring, according to the first embodiment of the present invention is further processed, whereby the exposed diffusion layer is removed at the upper and lower corners of the upper and lower surfaces of the outer circumferential surface by chamfering the corner regions located at the upper and lower corners before the ion-plating deposition layer is formed.
According to a second embodiment of the present invention, a piston ring is provided wherein the exposed diffusion layer is reduced in the thickness to 30% or less of the nitride layer on at the upper and lower corners of the upper and lower surfaces and the outer circumferential surface by chamfering the corner regions located at the upper and lower corners before the ion-plating deposition layer is formed.
When a piston ring is produced as described above, according to the present invention, cracks tends to occur in the ion-plating deposition layer on the upper and lower corner regions of the stainless steel base material of the piston ring, as in conventional piston rings, because the ion-plating deposition layer is lacing in toughness. However, in the piston ring according to the present invention, even when cracks actually occur in the ion-plating deposition layer, such cracks would not propagate to areas below the deposition layer, because right under the ion-plating deposition layer, there exists a zone that would not allow cracks to propagate therethrough, that is, depending on the case, either the non-nitrided region of the stainless steel base material or an area located deepest in the diffusion layer that is little nitrided.
Specifically, in case that, according to the first embodiment of the present invention, the upper and lower corner regions of the nitride layer of the piston ring is chamfered deep enough to remove an entire nitride layer to expose the stainless steel base material on the upper and lower corner regions thereof, cracks occurring in the ion-plating deposition layer are definitely unlikely to propagate below because the non-nitrided stainless steel base material that would not allow cracks to propagate therethrough is located right under the ion-plating deposition layer.
However, in case where the axial length or thickness of the piston ring is relatively small, whereby deep chamfering could deteriorate the sealing capability of the piston ring, then, preferably, the corner chamfering process is conducted to the extent such that the exposed diffusion layer remains in thickness equal to 30% or less of the nitride layer in the original thickness thereof at the upper and lower corner regions of the outer circumferential surface, according to the second embodiment of the present invention.
In order to improve the crack preventive capability of the ion-plating deposition layer, the crystal state of the layer is preferably arranged so as to have a columnar structure with the crystal orientation at [200].
With a piston ring implemented as described above, an advantage is effected in that degradation of the fatigue strength is prevented that otherwise would be caused by cracks occurring in the ion-plating deposition layer of the piston ring.
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Chinou Minako
Ogawa Katsuaki
Knight Anthony
Nippon Piston Ring Co. Ltd.
Peavey E
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