JP2002039384A - piston ring - Google Patents

Abstract

(57) [Problem] To provide a piston ring which does not cause cracking or peeling of a surface treatment layer on a barrel-like sliding surface of a piston ring operating under severe output conditions. SOLUTION: The sliding surface 4 has an outer peripheral barrel shape, an upper surface 5 facing the engine combustion chamber side, and a lower surface 6 facing the engine crankcase side, and a corner between the sliding surface, the upper surface, and the lower surface. Is a piston ring having a corner portion 4B in a shape from which a corner is removed, and the corner portion 4B has a radius of 0.0
It has a curved surface shape of 5 mm or more and smaller than the radius of the barrel portion 4A. Further, the corner portion and the barrel portion are continuously connected without any ridge line portion. The barrel part and the corner part are formed of a nitrided layer or a PVD layer or both layers, and the thickness of the corner part nitrided layer or the PVD layer is less than half the thickness of the barrel surface nitrided layer or the PVD layer. is there.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring,
In particular, the present invention relates to a piston ring having a sliding surface whose outer periphery forms a barrel shape.

[0002]

2. Description of the Related Art A piston receives a force oblique to the axial direction of a cylinder via a piston rod due to the rotational movement of a crankshaft. Therefore, even when the piston ring mounted on the piston slides on the cylinder, an oblique force acts on the cylinder axis direction.
In consideration of the above, as shown in FIG.
The outer peripheral sliding surface 104 of 01 is polished into a barrel surface shape by lapping or the like in order to improve the sliding relationship with the cylinder. That is, the outer diameter of the central portion of the piston ring in the axial direction is maximum, and gradually toward the upper surface 105 facing the engine combustion chamber side of the piston ring, and gradually toward the lower surface 106 facing the engine crankcase side of the piston ring. The outer diameter of the barrel is reduced. Further, there is an eccentric barrel-shaped piston ring in which a maximum outer diameter portion is shifted from an axial center portion of the piston ring.

Here, in order to prevent the barrel-shaped end portion, that is, the portion where the barrel surface 104A intersects the upper surface 105 and the lower surface 106, from exerting an adverse effect on the cylinder, such as galling, on sliding. In general, the intersection is formed into a corner 104B which is chamfered into a flat shape, and the intersection is formed at an obtuse angle.

In order to manufacture a piston ring base material, there is a method of bending a steel wire having a rectangular cross section. Here, in the production of a steel wire, a drawing process or a rolling process is performed. In order to facilitate these processes, the cross section of the wire after the drawing or the rolling is not a square, as shown in FIG. Four corners 2 of wire 200
04 has an obtuse-angled shape. Then, the wire 200 is bent into a ring shape, and a portion corresponding to the outer peripheral surface is polished to form a barrel surface.

Further, a piston ring for a high-speed, high-power engine is generally provided with a surface treatment layer, such as a nitride layer 107 or a PVD layer, on the barrel-like sliding surface in order to enhance the wear resistance and scuffing resistance of the outer peripheral surface. Or both layers are formed. To perform these surface treatments, it is necessary to clean the piston ring base material, but since sludge-like processing scum and oil generated during barrel surface processing tend to remain at the barrel surface end, The chamfering described above is also advantageous in that these residues can be removed.

[0006]

However, in the conventional piston ring 101, as shown in FIG. 7, the boundary between the planar corner portion 104B and the barrel surface 104A forms an obtuse angle and still has an irregular shape like a ridgeline. Continuous edge 10
4C is present. When such a ring is operated under severe high temperature and high pressure conditions, the nitride layer or PVD layer peels off at the edge portion 104C, or the edge portion 104C becomes a starting point of crack generation, and the inside of the nitride layer 107 or PVD layer It was found that cracks propagated and the piston ring was damaged.

Accordingly, an object of the present invention is to provide a piston ring which does not cause cracking or peeling of the surface treatment layer on the barrel-like sliding surface of the piston ring operating under severe output conditions.

[0008]

In order to achieve the above object, the present invention provides a sliding surface having an outer peripheral barrel shape, an upper surface facing an engine combustion chamber, and a lower surface facing an engine crankcase. A piston ring having a corner having a shape in which a corner between the sliding surface and the upper surface and a corner between the sliding surface and the lower surface are removed, wherein the corner has a radius of 0.05 mm. As described above, a piston ring having a curved surface shape smaller than the barrel surface radius and having the corner portion and the barrel surface continuously connected without any ridge line portion is provided.

Here, a nitride layer is formed at least on the barrel surface and the corner portion, and the thickness of the nitride layer at the corner portion is not more than 1/2 of the thickness of the nitride layer on the barrel surface. Is preferred.

[0010] Alternatively, a PVD layer is formed on the nitrided layer, and the thickness of the PVD layer at the corner portion is equal to the thickness of the barrel surface.
It is preferable that the thickness is not more than 1/2 of the thickness of the VD layer.

Alternatively, a PVD layer is directly formed on at least the barrel surface and the corner portion, and the PVD layer is formed on the corner portion.
The thickness of the layer is preferably not more than half the thickness of the PVD layer on the barrel surface.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A piston ring according to a first embodiment of the present invention will be described with reference to FIGS. The piston ring base material is made of steel, and has a substantially square cross section as shown in FIG. This cross-sectional shape is not a perfect rectangle, and the circumferential length of the piston ring base material on the inner circumferential surface 3 side is shorter than the circumferential length on the outer circumferential surface 4 side, so that the upper surface 5 and the lower surface 6 are not parallel to each other. , So that the distance between the upper and lower surfaces becomes shorter inward in the radial direction. The upper surface 5 faces the engine combustion chamber, and the lower surface 6 faces the engine crankcase. The piston ring 1 having such a shape is generally called a keystone ring.

The outer peripheral surface 4 of the piston ring 1 has the largest outer diameter at the axially central portion or approximately the central portion of the piston ring, and gradually moves toward the upper surface 5 of the piston ring and gradually toward the lower surface of the piston ring. It has a barrel portion 4A having a barrel shape whose diameter decreases. Further, a corner portion 4B where the end portion of the barrel portion 4A intersects the upper surface 5 and the lower surface 6 has a curved surface shape having a radius R1 smaller than the barrel portion radius R as shown in FIG. The barrel 4A is continuously connected to the barrel 4A without any ridges (edges).

The above piston ring base material 2 has a nitride layer 7
Is formed. Here, the nitrided layer 7 is formed on the entire surface of the piston ring base material 2, and the thickness t1 of the nitrided layer 7 at the corner 4B is one of the thickness t2 of the nitrided layer at the barrel 4A.
/ 2 or less. If the thickness exceeds １ ／, the stress inherent in the nitrided layer 7 cannot be sufficiently reduced, and an excessive load acts on the nitrided layer at the corner 4B, and the nitrided layer has sufficient fatigue strength. To avoid it because you will not be prepared.

The corner 4B after the formation of the nitride layer has a curved shape having a radius of 0.05 mm or more and smaller than the barrel radius R, and the corner 4B and the barrel 4A have no ridge. They are formed continuously. The reason why the radius of the corner portion is 0.5 mm or more is that if the radius is less than this value, the boundary with the barrel portion becomes discontinuous and an edge may be present.

In manufacturing the piston ring having the above structure, the entire outer peripheral surface of the piston ring base material is polished into a barrel shape by lapping or the like. At this time, the corner portion is further polished into a curved shape so that the radius of the corner portion is smaller than the radius of the barrel surface, and the corner equivalent portion and the barrel surface are ridged (edge). (Part) may be continuously connected to each other without being present.

Next, a nitriding treatment 7 is performed on the entire surface of the piston ring base material 2 to form a nitrided layer having a uniform thickness over the entire circumference of the base material, and then the final outer peripheral shape of the piston ring as shown in FIG. The outer peripheral surface of the piston ring is polished using the grindstone 8. As shown in FIG. 1, the thickness t1 of the nitride layer 7 at the corner 4B is reduced by polishing to the nitride layer 7 at the barrel 4A.
2, the radius R1 of the corner portion 4B is 0.05 mm or more and smaller than the radius R of the barrel portion 4A, as shown in FIG. A continuous shape can be obtained without a ridge at the boundary between 4B and barrel 4A.

According to the above configuration, since the corner portion 4B and the barrel portion 4A are continuously connected to each other and there is no edge portion such as a ridge line at the boundary between the two, the corner portion 4B and the barrel portion 4A are not connected. The boundary with 4A cannot be a starting point of the crack generation of the nitrided layer 7, and the possibility of the chipping of the nitrided layer 7 can be reduced. Further, the thickness of the nitride layer 7 at the corner 4B is set to 1 / th of the thickness of the barrel 4A.
Since the number is set to 2 or less, the nitrided layer 7 can have sufficient fatigue strength.

A piston ring 11 according to a second embodiment of the present invention will be described with reference to FIG. The second embodiment also relates to a keystone ring, and a PVD layer 19 is provided on the outer peripheral sliding surface (barrel portion and corner portion) of the piston ring base material 12 instead of the nitride layer. In the second embodiment, a nitride layer 17 having a uniform thickness is formed on the upper surface 15, the lower surface 16, and the inner peripheral surface 13 of the piston ring 11. Then, a PVD layer 19 is formed on the barrel portion 14A and the corner portion 14B. Here, the outer peripheral surface of the PVD layer 19 has a barrel surface shape and a corner portion 14B.
Has a radius of at least 0.05 mm, is smaller than the radius of the barrel portion 14A, and has a corner portion 14A.
B and the barrel portion 14A have such a shape that they are continuously connected to each other without any ridge portion (edge portion). Further, the thickness of the PVD layer 19 in the corner portion 14B is not more than の of the thickness of the PVD layer 19 in the barrel portion 14A. If the thickness exceeds １ ／, the stress existing in the PVD layer 19 cannot be reduced sufficiently, and
This is because an excessive load acts on B and the PVD layer 19 does not have sufficient fatigue strength.

In manufacturing the piston ring having the above structure, an unillustrated nitriding agent is applied to the entire surface of the piston ring base material having a substantially rectangular cross section, and then the upper, lower, and inner peripheral surfaces are formed into desired shapes. Grind. At this time, the upper surface, the lower surface, and the portion corresponding to the inner peripheral surface of the nitride inhibitor are removed. Next, when a nitriding process is performed on the base material, a nitride layer is formed on the upper surface, the lower surface, and the inner peripheral surface. Next, the entire outer peripheral surface of the piston ring base material is polished into a barrel surface shape by lapping or the like, and the corner portion is further polished into a curved surface shape, so that the radius of the corner portion is smaller than the radius of the barrel surface. In addition to having a small curved surface shape, the corner portion and the barrel surface are formed to be continuously connected to each other without any ridge portion (edge portion). Finally, a PVD layer is formed on the barrel surface and the corner. In this case, a large number of piston ring base materials are aligned coaxially in the axial direction, and the film is formed in a state where the outer peripheral surfaces are aligned. Here, since the film formation has directionality, PV
The D layer is formed thin at the corner portion and thick at the barrel portion.

Also in the second embodiment, the corner portion 14B and the barrel portion 14A are continuously connected and formed, and since there is no edge portion such as a ridgeline at the boundary between the two, the corner portion 14B And barrel section 14A
Can not be the starting point of the crack generation of the PVD layer 19, and the possibility of the chipping of the PVD layer 19 can be reduced. Further, since the thickness of the PVD layer 19 at the corner portion 1B is set to １ ／ or less of the thickness of the barrel portion 14A, the stress inherent in the PVD layer 19 can be reduced during the formation of the PVD layer, and the PVD layer can be sufficiently formed. High fatigue strength.

FIG. 5 is a graph showing the ratio of the thickness of the nitrided layer in the corner portion and the barrel portion and the fracture resistance index when the radius of the corner portion is changed in the piston ring according to the present invention. It is a graph which shows a productivity index. Sample 1 is a comparative example. Table 1 shows the ratio (t2 / t1) of the thickness of the nitrided layer between the corner portion and the barrel portion and the radius R1 of the corner portion in Samples 1 to 4. Sample 4 is a case where the nitrided layer in the barrel portion and the corner portion is completely removed, and is in a state before the formation of the PVD layer in the second embodiment. By using a grindstone as shown in FIG. 3 and changing the grinding amount, the ratio (t2 / t1) of the thickness of the nitrided layer between the corner portion and the barrel portion in Samples 1 to 4 can be obtained.

Table 1 t2 / t1 R1 (mm) Sample 1 2/3 0.05 Sample 2 1/2 0.30 Sample 3 1/3 0.30 Sample 4 0/1 0.30

Many of the above samples 1 to 4 were manufactured and set on a fatigue strength tester to obtain a breakage resistance index. Samples 2 to 4 were found to have significantly improved breakage index as compared to sample 1.

Further, with respect to the above-mentioned samples 1 to 4, the productivity index, which means the percentage of non-defective products as non-defective products, was examined. It was also found that Samples 2 to 4 were significantly improved in productivity index as compared to Sample 1.

The piston ring according to the present invention is not limited to the embodiment described above, and various modifications and improvements can be made within the scope described in the claims. For example, in the first embodiment, only the nitride layer 7 is formed on the outer peripheral surface side of the piston ring, and in the second embodiment, the PVD layer 1 is formed.
Although only 9 is formed, a nitride layer may be formed first, and a PVD layer may be formed thereon. In this case, the thickness of the nitrided layer at the corner portion is not more than １ ／ of the thickness of the nitrided layer at the barrel surface, and the thickness of the corner portion of the PVD layer on the nitrided layer is the thickness of the PVD layer at the barrel surface. １ ／ or less. Thereby, the fatigue strength of both the nitrided layer and the PVD layer can be secured.

[0027]

According to the piston ring of the first aspect, the corner portion has a curved surface shape having a radius of 0.05 mm or more and smaller than the barrel surface radius, and the corner portion and the barrel surface have a ridge portion. Since it is continuously connected without forming, the boundary between the corner and the barrel cannot be the starting point of crack generation in the nitrided layer or PVD layer, and the possibility of chipping in the layer may be reduced. Can be reduced.

According to the piston ring of the second aspect,
A nitride layer is formed at least on the barrel surface and the corner,
Since the thickness of the nitrided layer at the corner portion is not more than の of the thickness of the nitrided layer at the barrel surface, the nitrided layer can have sufficient fatigue strength. According to the piston ring of the third aspect, the PVD layer is formed on the nitrided layer, and the thickness of the PVD layer at the corner portion is set to １ ／ or less of the thickness of the PVD layer at the barrel surface. Not only the nitride layer but also the PVD layer can have sufficient fatigue strength.

According to the piston ring of the fourth aspect,
A PVD layer is formed directly on at least the barrel surface and the corners, and the thickness of the PVD layer on the corners is determined by the PV of the barrel surface.
Since the thickness of the D layer is １ ／ or less, the PVD layer can have sufficient fatigue strength.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a piston ring according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing a barrel portion and a corner portion of the piston ring according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing the process of manufacturing the piston ring according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a piston ring according to a second embodiment of the present invention.

FIG. 5 is a graph showing a fracture resistance index of the piston ring according to the first embodiment of the present invention when the ratio of the thickness of the nitrided layer in the corner portion and the barrel portion and the radius of the corner portion are changed, and in a comparative example. .

FIG. 6 is a graph showing the productivity index of the piston ring according to the first embodiment of the present invention when the ratio of the thickness of the nitrided layer in the corner portion and the barrel portion and the radius of the corner portion are changed, and in a comparative example. .

FIG. 7 is a cross-sectional view showing a conventional piston ring having a ridge (edge) at a boundary between a barrel and a corner.

FIG. 8 is a sectional view showing a conventional wire for a piston ring.

[Explanation of symbols]

 1, 11 Piston ring 4A, 14A Barrel part 4B 14B Corner part 5, 15 Upper surface 6, 16 Lower surface 7, 17 Nitride layer 19 PVD layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // C23C 8/24 C23C 8/24

Claims (4)

[Claims] A sliding surface having an outer peripheral barrel shape, an upper surface facing the engine combustion chamber side, and a lower surface facing the engine crankcase side, and a corner between the sliding surface and the upper surface; A piston ring having a corner portion in which a corner between a sliding surface and the lower surface is removed, wherein the corner portion has a curved surface shape having a radius of 0.05 mm or more and smaller than a barrel surface radius, and The piston ring, wherein the portion and the barrel surface are continuously connected without a ridge portion. 2. A nitride layer is formed on at least the barrel surface and the corner, and the thickness of the nitride layer on the corner is:
2. The piston ring according to claim 1, wherein the thickness of the piston ring is 1/2 or less of the thickness of the nitrided layer on the barrel surface. 3. A PVD layer is formed on the nitride layer,
The thickness of the PVD layer at the corner is the PVD of the barrel surface.
3. The structure according to claim 2, wherein the thickness is not more than 1/2 of the thickness of the layer.
The described piston ring. 4. A PVD layer is formed directly on at least the barrel surface and the corner, and the thickness of the PVD layer at the corner is not more than half the thickness of the PVD layer on the barrel surface. The piston ring according to claim 1, wherein: