JP4761375B2 - Piston ring for internal combustion engine - Google Patents

Description

  The present invention relates to a piston ring for an internal combustion engine that is used by being mounted in a ring groove provided in a piston of the internal combustion engine, and particularly relates to a piston ring for an internal combustion engine that has high breakage resistance and excellent wear resistance.

  A piston ring used in an internal combustion engine is incorporated into a piston ring groove disposed in a reciprocating manner in a cylinder liner of the engine so that the outer peripheral surface thereof and the inner peripheral surface of the cylinder liner are in a sliding contact relationship. The piston ring mainly functions to seal the combustion chamber during engine operation, control the thickness of the lubricant film formed on the cylinder surface, and cool the piston by transferring combustion heat from the piston to the cylinder liner. To do. Therefore, the piston ring is required to have high characteristics such as wear resistance, seizure resistance, heat resistance, and oil retention.

  Conventionally, the outer peripheral sliding surface of a piston ring for an internal combustion engine has been subjected to surface treatment for the purpose of improving wear resistance such as hard chrome plating treatment or nitriding treatment in order to improve its durability. . However, in recent years, internal combustion engines have become increasingly lighter and more powerful, and the sliding environment of the piston ring has become extremely harsh. Surface treatment such as that described above has sufficient wear resistance and other functions. Can no longer be satisfied. Recently, for the purpose of further extending the life of the piston ring, a piston ring having a hard coating (chromium nitride, titanium nitride, etc.) formed by an ion plating method on the outer peripheral sliding surface is used. In addition, in order to improve the breakage resistance of the piston ring, an ion plating film is formed only on the outer peripheral sliding surface, and a nitride layer is formed only on the upper and lower surfaces and the inner peripheral surface, thereby nitriding the base of the ion plating film. A piston ring of a type that suppresses the propagation of cracks without any treatment is used.

  Since the piston ring as described above forms a hard film on the outer peripheral sliding surface by ion plating, and then performs nitriding treatment on the upper and lower surfaces and the inner peripheral surface, the hard film is emptied during nitriding. Nitrogen penetrates from the hole to the outer peripheral surface of the base material, and the base material is nitrided, so that a hard nitrided layer enters between the base material and the hard coating, and the breakage resistance of the part decreases. There is a case. In particular, at both end portions of the outer peripheral sliding surface, the thickness of the hard coating is thinner than that of the central portion of the outer peripheral sliding surface, so that nitrogen easily enters and the breakage resistance is reduced.

  Therefore, in Patent Document 1, a nitriding prevention layer is formed on the outer peripheral sliding surface, and then the piston ring is subjected to nitriding treatment. After the nitriding treatment, the nitriding preventing layer is removed, and the outer peripheral sliding surface is hardened by an ion plating method. By forming the film, nitriding of the outer peripheral sliding surface is prevented. However, the above method requires the formation and removal of the nitriding prevention layer, which leads to an increase in manufacturing steps and an increase in production cost, and cannot be said to be a practical method. Regarding fatigue strength improvement, there is a description that a nitrided layer is not formed to prevent the propagation of cracks, but a description of the ratio between the axial length of the corner (chamfered portion) and the thickness of the nitrided layer, etc. There is no.

  In Patent Document 2, after forming a hard film by ion plating on the outer peripheral sliding surface, the upper and lower surfaces and the inner peripheral surface are subjected to nitriding treatment, and the upper and lower surfaces of the piston ring are polished, whereby the hard film and the Vickers There is a disclosure of a piston ring characterized in that nitride layers having a hardness (HV) of 700 or more are separated from each other to improve fatigue strength. In this forming method, when a hard coating is formed on the outer peripheral sliding surface in a state where a plurality of piston rings are stacked in the axial direction, the ends of the outer peripheral sliding surface (upper and lower surfaces and outer peripheral sliding surface) Since the piston ring has a curved shape, a recessed space is formed at a location where the piston rings are adjacent to each other. When a hard coating is formed on the outer peripheral sliding surface of the piston ring in such a state, a hard coating is also formed on the recessed portion, and the hard coating 6 is formed on the upper and lower surfaces of the piston ring 1 as shown in FIG. A fogging portion 70 is generated. Since the formed cover part 70 varies for each piston ring 1, when the base material 2 having such a cover part 70 is subjected to nitriding treatment, the formed nitride layer also varies for each piston ring 1. Even if the upper and lower surfaces of the piston ring 1 are polished thereafter, the distance between the hard coating 6 and the nitride layer 10 having a Vickers hardness (HV) of 700 or more varies, which is not preferable in production.

  In Patent Document 2, there is a description that fatigue strength can be improved by separating a hard film and a nitride layer having a Vickers hardness (HV) of 700 or more from each other. The variation in distance is large, and it is difficult to stabilize the fatigue strength. In FIGS. 1 and 3 of Patent Document 2, a nitride layer having a Vickers hardness (HV) of 700 or more is formed over the entire corner portion (chamfered portion). This is because the film and the nitride layer having a Vickers hardness (HV) of 700 or more are separated from each other, and there is no description regarding the ratio between the axial length of the corner portion (chamfered portion) and the thickness of the nitride layer.

JP-A-5-172248 JP 2000-291800 A

  The present invention has been made in view of the above-mentioned problems, and has as its main object to provide a piston ring for an internal combustion engine that is less prone to crack propagation and has excellent breakage resistance and wear resistance. is there.

  In order to achieve the above object, the present invention provides a piston ring for an internal combustion engine that is mounted in a ring groove of a piston and slides with a cylinder liner or a cylinder bore, wherein the piston ring includes an outer peripheral sliding surface, upper and lower surfaces, A nitride layer is formed only on the upper and lower surfaces, or only on the upper and lower surfaces and the inner peripheral surface, and a hard film is formed on the outer peripheral sliding surface by an ion plating method. Piston ring axial direction of a nitride layer contact region having a Vickers hardness (HV) of 700 or more, which is a region where a nitride layer having a Vickers hardness (HV) of 700 or more in the nitride layer formed on the lower surface is in contact with the hard coating Is within the range of 3 to 40% of the length of the chamfered portion located at the upper end and the lower end of the outer peripheral sliding surface in the piston ring axial direction. To provide an internal combustion engine for a piston ring that.

  In the piston ring for an internal combustion engine of the present invention (hereinafter sometimes referred to as a piston ring), the length of the nitride layer contact region of 700 or more of the Vickers hardness (hereinafter sometimes referred to as HV) and the outer periphery sliding. Since the ratio of the length of the chamfered portion to the chamfered portion is within the above range and the ratio of the nitride layer of HV700 or higher in the chamfered portion is small, the breakage resistance of the chamfered portion can be improved.

  In the said invention, it is preferable that the film thickness of the said HV700 or more nitride layer exists in the range of 15-80 micrometers. This is because by setting the film thickness of the nitride layer of HV700 or more in the above range, a piston ring in which the ratio of the length of the nitride layer contact region of HV700 or more is in the above range can be easily formed.

  The present invention provides an effect that a piston ring for an internal combustion engine having high breakage resistance and excellent wear resistance can be obtained.

  A piston ring according to the present invention is a piston ring for an internal combustion engine that is mounted in a ring groove of a piston and slides with a cylinder liner or a cylinder bore. The piston ring has an outer peripheral sliding surface, an upper and lower surface, and an inner peripheral surface. A nitride layer is formed only on the upper and lower surfaces, or only on the upper and lower surfaces and the inner peripheral surface, and a hard film is formed on the outer peripheral sliding surface by an ion plating method, and is formed on the upper and lower surfaces. The length in the piston ring axial direction of the nitride layer contact region of HV700 or higher, which is a region where the nitride layer of the nitride layer having a Vickers hardness (HV) of 700 or higher and the hard coating is in contact, is the outer peripheral sliding surface. It is characterized in that it is within a range of 3 to 40% of the length in the piston ring axial direction of the chamfered portions located at the upper end and the lower end.

  Hereinafter, the piston ring of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of a piston ring of the present invention. As illustrated in FIG. 1, a hard coating 6 composed of a dense layer 4 and a porous layer 5 formed on the dense layer 4 on the outer peripheral surface of the base material 2 of the piston ring 1 of the present invention. Is formed. Further, a nitride layer 10 of HV700 or more is formed on the upper surface 7, the lower surface 8 and the inner peripheral surface 9 of the base material 2 of the piston ring other than the outer peripheral sliding surface 3 portion. In the present invention, h1 in FIG. 1 is the axial height of the piston ring, and a1 is the radial width of the piston ring.

  A chamfered portion is formed at each of the upper end and the lower end of the outer peripheral sliding surface of the piston ring of the present invention as described above. FIG. 2 shows a schematic cross-sectional view of an example of such a chamfered portion located at the upper end of the outer peripheral sliding surface. As illustrated in FIG. 2A, a chamfered portion 11 is formed on the upper surface 7 side of the outer peripheral sliding surface 3. Further, a region where the nitride layer 10 of HV700 or more formed on the upper surface 7 and the hard coating 6 formed on the outer peripheral sliding surface 3 are in contact is a nitride layer contact region 12 of HV700 or more. In the present invention, the piston ring axial length of the chamfered portion 11 is y, the piston ring axial length of the nitride layer contact region 12 of the HV700 or more is x, and the piston ring axial length of the nitride layer of the HV700 or more. Let z be the thickness of the nitride layer of HV700 or more.

Since the outer peripheral sliding surface is a surface that slides with the inner wall surface of the cylinder, the chamfered portion, which is a part of the outer peripheral sliding surface, is required to have high breakage resistance, but conventional piston rings improve wear resistance. For this reason, a nitride layer having high hardness is formed on the upper and lower surfaces, and the end portion of the nitride layer reaches the chamfered portion, so that the portion causes a decrease in breakage resistance of the chamfered portion. However, in the piston ring of the present invention, the ratio of the nitride layer contact region length x of HV700 or more to the chamfered portion length y is within the above range, and the ratio of the nitride layer of HV700 or more in the chamfered portion is small. Therefore, the influence of the nitride layer of HV700 or more formed on a very small part of the chamfered portion on the breakage resistance is small, and as a result, the breakage resistance of the chamfered portion can be improved. Further, since the nitrided layer of HV700 or higher is formed in the portion where the chamfered portion is adjacent to the upper and lower surfaces, the wear resistance of the upper and lower surfaces of the piston ring can be maintained.
Hereafter, each structure and manufacturing method of such a piston ring of this invention are each demonstrated in detail.

1. Nitride Layer In the piston ring of the present invention, a nitride layer is formed only on the upper and lower surfaces of the base material or on the upper and lower surfaces and the inner peripheral surface. This is because, by forming the nitride layer, it is possible to improve the wear resistance against the tapping of the upper and lower surfaces of the piston ring with the upper and lower surfaces of the piston ring groove. Such a nitrided layer has a high nitrogen concentration on the surface of the base material when nitrogen penetrates and diffuses from the surface of the piston ring into the base material by a general method, and enters the base material from the surface of the base material. As the nitrogen concentration decreases, a nitride layer with high hardness is formed near the surface of the base material, and a nitride layer with lower hardness is formed inside thereof. In the present invention, the “region where the nitride layer of HV700 or higher and the hard coating formed on the outer peripheral sliding surface are in contact” is formed on the surface of the base material of the nitride layer as described above. In addition, a region having a Vickers hardness (HV) of 700 or more and a region where the hard coating is in contact with each other. In the present invention, the Vickers hardness (HV) of 700 or more means that the value obtained when the test load of the Vickers hardness tester is 0.9807 N (100 gf) is 700 or more.

  As described above, the nitride layer of HV700 or higher formed on the upper and lower surfaces of the piston ring of the present invention has the piston ring axial length of the chamfered portion y, and the piston ring axial length of the nitride layer contact region of HV700 or higher. When the thickness is x (see FIG. 2), the nitride layer contact region length x of HV700 or more is in the range of 3-40% of the chamfered portion length y, preferably in the range of 5-20%. Formed. If the ratio between the nitride layer contact region length x of HV700 or more and the chamfered portion length y is less than the above range, the nitride layer contact region of HV700 or more may be too small to be formed uniformly. On the other hand, if the ratio exceeds the above range, the effect of improving the breakage resistance of the chamfered portion may not be sufficiently obtained. The actual measured value of the nitride layer contact region length x of HV700 or more at this time varies greatly depending on the dimensions of the piston ring used and the chamfered portion to be formed, but is usually in the range of 5 to 80 μm, preferably 7 It is formed within a range of ˜30 μm.

  In the present invention, the nitride layer of HV700 or more can be formed in an arbitrary form. For example, as illustrated in FIG. 2A, the nitride layer 10 of HV700 or more in the entire region in the thickness (depth) direction. The nitride layer 10 of HV700 or higher and the hard coating 6 may not be in contact, and may be in contact only on the outermost periphery of the upper surface 7 of the base material 2. Further, as illustrated in FIG. 2B, the nitride layer 10 of HV700 or higher and the hard coating 6 may be in contact with each other in the entire thickness direction of the nitride layer 10 of HV700 or higher. In this case, the length x of the nitride layer contact region 12 above HV700 and the film thickness (depth) z of the nitride layer 10 above HV700 are the same length. The same applies to the chamfered portion on the lower surface side located at the lower end of the outer peripheral sliding surface.

  The film thickness of such a nitride layer of HV700 or higher is not particularly limited, but is preferably in the range of 15 to 80 μm, and more preferably in the range of 20 to 70 μm. This is because by setting the film thickness within the above range, a nitride layer of HV700 or more having a ratio of the nitride layer contact region length x of HV700 or more as described above can be easily formed.

2. Hard Film In the present invention, the hard film formed on the outer peripheral sliding surface is not particularly limited, and a known film that can obtain desired breakage resistance can be used. Among them, in the present invention, the hard coating is composed of a dense layer made of metal and / or ceramics formed on the outer peripheral surface of the piston ring base material, and a porous layer formed on the dense layer. It is preferable. By providing the dense layer, nitriding of the outer peripheral surface of the base material can be prevented even when the base material is subsequently nitrided. Further, by forming a porous layer having good adhesion to the dense layer and high breakage resistance on the dense layer, the breakage resistance of the outer peripheral sliding surface can be improved.
Hereinafter, such a dense layer and a porous layer will be described in detail.

(A) Dense layer In the present invention, on the surface of the outer peripheral surface of the base material of the piston ring, a dense layer that is a dense layer made of metal and / or ceramics is within a range of 1 to 5 μm by ion plating. Especially, it is preferable to form with the film thickness in the range of 2-4 micrometers. If the film thickness of the dense layer is less than the above range, the nitrogen intrusion prevention function is insufficient, and a nitride layer may be formed under the dense layer. On the other hand, an unnecessarily thick dense layer whose film thickness exceeds the above range is not desirable in terms of production efficiency because it takes time to form, and is not desirable from the viewpoint of material cost.

  The metal used for forming the dense layer is not particularly limited as long as it can form a dense layer capable of preventing intrusion of nitrogen, and is usually a single metal or a plurality of metals. An alloy containing is used. In the present invention, from the viewpoint of adhesion with the base material of the piston ring, thermal expansion coefficient, flexibility, etc., Cr, Cr-based alloy, Ti, Ti-based alloy, etc., among others, Cr, Cr-based alloy (Cr-B alloy, Cr-V-B alloy, Cr-B-Si alloy, etc.) are preferably used. By forming a dense layer using such a metal having intermediate properties between the base material and the porous layer, the adhesion between them can be improved, and the base material, the porous layer, It is possible to prevent peeling due to a difference in thermal expansion coefficient between the two.

Further, when the dense layer is made of ceramics, it can be formed with the same film thickness as that of the metal. Such a dense layer made of ceramics can form a dense Cr ₂ N layer as an ion plating film, for example, by introducing nitrogen into a furnace of an ion plating apparatus.

  The dense layer may be a layer made only of metal, a layer made only of ceramics, or a layer made of metal and ceramics. The dense layer may have a multilayer structure in which a layer made of only ceramics is formed on a layer made of only metal, for example.

  The degree of denseness of the dense layer is not particularly limited as long as it can inhibit the penetration of nitrogen into the base material under the dense layer and prevent nitridation of the base material during nitriding. Is not to be done. In the present invention, the porosity of the dense layer is preferably in the range of 0 to 0.4% in order to effectively inhibit nitrogen intrusion.

(B) Porous layer In the present invention, a porous layer is preferably formed on the dense layer described above by an ion plating method. Since the porous layer is a layer having pores that absorb stress, by forming such a porous layer on the outer peripheral sliding surface of the piston ring, the fracture resistance of the outer peripheral sliding surface is improved. be able to.

  The porosity of the porous layer used in the present invention is preferably formed in the range of 0.5 to 20.0%, particularly in the range of 1.0 to 10.0%. When the porosity of the porous layer is less than the above range, the amount of pores that absorb stress is not sufficient, and preferable breakage resistance may not be obtained. On the other hand, when the porosity exceeds the above range, there is a possibility that the strength of the porous layer is lowered due to too many pores.

The material for forming the porous layer is not particularly limited as long as it can form a layer having a porosity as described above. In general, an inorganic material such as a metal nitride is used. Among them, a metal nitride forming the dense layer, for example, a Cr-N-based material, a Cr-B-N-based material, a Cr-B-Si-N-based material, or a Ti-N-based material is preferably used. In particular, CrN, Cr ₂ N, a mixture of CrN and Cr ₂ N, a mixture of Cr and CrN, a mixture of Cr and Cr ₂ N, a mixture of Cr, CrN and Cr ₂ N, or TiN are preferably used. It is done. By forming a porous layer using such a material, a porous layer having characteristics close to that of the dense layer can be formed, so that adhesion to the dense layer can be improved, and the dense layer and It is possible to prevent the peeling due to the difference in the thermal expansion coefficient.

  The film thickness of the porous layer is not particularly limited as long as desired fracture resistance can be obtained, and is usually in the range of 5 to 80 μm, preferably in the range of 10 to 50 μm. It is formed.

3. Base Material A chamfered portion is formed on the outer peripheral surface of the base material of the piston ring used in the present invention. By providing such a chamfered portion, the breakage resistance of the outer peripheral sliding surface can be improved. The size of the chamfered portion is not particularly limited, but the length in the axial direction of the piston ring (y in FIG. 2) is the height in the axial direction of the piston ring (in FIG. 1) from the viewpoint of improving breakage resistance. It is preferably formed within a range of 5 to 30% of h1), particularly within a range of 5 to 20%.

  The base material used for the piston ring of the present invention has a maximum height roughness Rz on the outer peripheral surface in the range of 1.0 to 4.0 [mu] m, particularly in the range of 1.5 to 2.5 [mu] m. It is preferable. If the maximum height roughness Rz of the outer peripheral surface of the base material is less than the above range, the surface area of the base material may be too small, and the adhesion with the dense layer formed thereon may deteriorate. On the other hand, if the maximum height roughness Rz exceeds the above range, it is difficult to form the dense layer with a uniform thickness when forming the dense layer by the ion plating method. The film thickness may be thin or not formed. In such a case, during the nitriding process, the dense layer has a thin film thickness, or nitrogen enters from a portion where the dense layer is not formed, and a nitride layer is formed on the base material under the dense layer, thereby forming the dense layer. This is not preferable because the obtained effect cannot be obtained sufficiently.

  Here, the maximum height roughness Rz is the sum of the maximum value of the peak height Zp and the maximum value of the valley depth Zv of the contour curve (roughness curve) at the reference length based on JIS B 0601: 2001. This value is expressed in micrometers (μm).

  The material of the base material is not particularly limited as long as it has the maximum height roughness Rz as described above, and a material generally used for piston rings can be used. For example, martensitic stainless steel represented by SUS440B or DINX90, SUS410 material, SUS440 material, 10Cr steel (Cr: 9 to 11% by mass), austenitic stainless steel, or the like can be used.

  In addition, the shape, dimensions, and the like of the base material other than the above are not particularly limited, and can be appropriately adjusted according to the use of the piston ring.

4). Manufacturing Method The manufacturing method of the piston ring of the present invention is not particularly limited as long as the piston ring having the above-described configuration can be obtained. For example, an ion plating method is applied to the outer peripheral surface of the base material of the piston ring. Can be produced by forming a hard film composed of the dense layer and the porous layer, polishing the upper and lower surfaces of the piston ring, and performing nitriding to form a nitride layer of HV700 or higher. Hereinafter, each process of the manufacturing method of such a piston ring is demonstrated.

(A) Formation of hard film by ion plating method In this step, a hard film composed of the dense layer and the porous layer can be formed on the outer peripheral surface of the base material of the piston ring by the following method. .
First, prior to the formation of the dense layer, the base material is heated within a range of 300 to 660 ° C. with a furnace heater of an arc ion plating apparatus set to a vacuum degree of 8 × 10 ⁻⁵ Torr or less. The gas adsorbed on the base material is released. Thereafter, a bias voltage in the range of −1000 to −600 V is applied to the base material, and arc discharge is generated between the cathode metal target and the anode to vaporize and ionize the metal of the target. Alternatively, the surface of the base material was cleaned by introducing argon gas and performing ion bombardment. In this case, a metal target forming a dense layer is used as the cathode target.

Argon gas is introduced into the furnace in which arc discharge is generated after the cleaning is performed until it falls within the range of 4 × 10 ⁻³ to 4 × 10 ⁻² Torr, and is set to −10 to −50V. A dense layer is formed on the outer peripheral surface of the base material by applying a bias voltage within the range. Further, a porous layer is formed on the dense layer by introducing a nitrogen gas until it falls within a range of 4 × 10 ⁻³ to 4 × 10 ⁻² Torr and applying a bias voltage within a range of −10 to −50 V. Can be formed.

(B) Polishing process When the hard film is formed by the above method, the hard film may be formed in places other than the outer peripheral surface such as the upper surface and the lower surface of the base material. When a hard film is formed on the upper and lower surfaces of the base material, the hard film inhibits the penetration of nitrogen into the base material, and a nitride layer of HV700 or more is uniformly formed on the upper and lower surfaces of the base material during the subsequent nitriding treatment. Since it may become impossible to form, it is preferable to polish the upper surface and the lower surface of the base material within the range of 10 to 20 μm, particularly within the range of 10 to 15 μm after the hard coating is formed. By performing such a polishing process and removing the cover portions of the hard film formed on the upper and lower surfaces, a nitride layer of HV700 or more can be formed uniformly and stably on the upper and lower surfaces of the base material.

(C) Nitriding treatment In the present invention, the piston ring having the hard film formed on the outer peripheral surface of the base material is subjected to nitriding treatment so that the upper and lower surfaces, or the upper and lower surfaces and the inner peripheral surface of the piston ring are HV700 or more. Nitride layers can be formed. The nitriding method is not particularly limited as long as it can form a nitride layer of HV700 or more as described above. Gas nitriding method (60 to 300 minutes at 550 to 600 ° C.), salt It can be performed by a known method such as a bath nitriding method (10 to 300 minutes at 570 to 590 ° C.). The formed nitrided layer having a Vickers hardness (HV) of 700 or more can be confirmed by polishing the cut surface of the piston ring to a mirror surface by polishing and finishing, and etching with 4% nital liquid. The detailed hardness distribution of the formed nitride layer can be confirmed by measuring the cross-sectional hardness by a method based on JIS G 0562: 1993.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Examples 1 to 14]
Piston ring base material (equivalent to SUS410 material, C: 0.65) having a diameter φ of 90 mm, a radial width (a1 shown in FIG. 1) of 2.7 mm, and an axial height (h1 shown in FIG. 1) of 1.0 mm. % By mass, Si: 0.40% by mass, Mn: 0.35% by mass, P: 0.03% by mass or less, S: 0.03% by mass or less, Cr: 13.5% by mass, Mo: 0.3 The chamfered portion length (y shown in FIG. 2) of each piston ring was set to the length shown in Table 1 below. A dense layer and a porous layer are formed on the outer peripheral surface of the base material by subjecting these piston rings to hard coating formation, polishing, and nitriding by the method described in “4. Manufacturing Method” above. A piston ring having nitride layers formed on the upper and lower surfaces and the inner peripheral surface was manufactured. At that time, a Cr target was used as the cathode of the arc ion plating apparatus. The formed dense layer was made of Cr, the film thickness was 5 μm, and the porosity was 0 to 0.2%. The porous layer formed on the dense layer was made of a mixture of Cr, CrN, and Cr ₂ N, and had a film thickness of 20 μm and a porosity of 1 to 7%. Further, after the formation of the porous layer, the upper and lower surfaces of the piston ring were each polished by 15 μm, and then nitriding was performed.

The nitriding treatment was performed by a salt bath soft nitriding method or a gas nitriding method with a target nitriding layer thickness of HV700 or more being 20 μm, 40 μm or 70 μm. For the salt bath soft nitriding method, a known salt bath is used at 580 ° C., and a nitride layer having a thickness of HV700 or more of 20 μm (Examples 1 to 3) is 0.33 hours, and a nitride layer of HV700 or more. For those having a thickness of 70 μm (Examples 8 to 10), nitriding treatment was performed for 3 hours. For the above gas nitriding method, at 550 ° C., the nitride layer of HV700 or more having a thickness of 40 μm (Examples 4 to 7) has a thickness of 60 minutes, and the nitride layer of HV700 or more has a thickness of 70 μm ( In Examples 11 to 14, the nitriding treatment was performed for 3 hours. Table 1 below shows the method of nitriding treatment in each example, the actual measured value of the formed nitride layer thickness of HV700 or more, the chamfered portion length y, and the nitrided layer contact area length of HV700 or more relative to the chamfered portion length y. The ratio (%) of x is shown.
The formed nitrided layer was confirmed and measured for cross-sectional hardness by the method described in “4. Manufacturing method (c) Nitriding treatment” to obtain a nitrided layer contact region length x of HV700 or more. It was.

[Comparative Example 1]
By forming a hard film, polishing, and nitriding in the same manner as in the above example, a dense layer and a porous layer are formed on the outer peripheral surface of the base material, and a nitride layer is formed on the upper and lower surfaces and the inner peripheral surface. Manufactured piston rings. When forming the nitride layer, nitriding treatment was performed at 550 ° C. for 5 hours by a gas nitriding method. Table 1 shows measured values of nitride layer thickness of HV700 or more formed, chamfered portion length y, and ratio (%) of nitride layer contact region length x of HV700 or more to chamfered portion length y.

[Comparative Example 2]
By forming a hard film, polishing, and nitriding in the same manner as in the above example, a dense layer and a porous layer are formed on the outer peripheral surface of the base material, and a nitride layer is formed on the upper and lower surfaces and the inner peripheral surface. Manufactured piston rings. When forming the nitride layer, nitriding treatment was performed at 580 ° C. for 0.25 hours by a salt bath soft nitriding method. Table 1 shows measured values of nitride layer thickness of HV700 or more formed, chamfered portion length y, and ratio (%) of nitride layer contact region length x of HV700 or more to chamfered portion length y.

[Comparative Examples 3 to 6]
Nitriding treatment was performed on the entire surface (outer peripheral surface, inner peripheral surface, upper surface and lower surface) of the piston ring base material having the same dimensions and materials as in the above example. The nitriding treatment was performed in the same manner as in the above-described example by a salt bath soft nitriding method or a gas nitriding method with a target thickness of a nitride layer of HV700 or more being 40 μm or 70 μm. After the compound layer (white layer) formed on the outermost surface of the base material by the nitriding treatment is removed by chemicals, a mixture of Cr, CrN, and Cr ₂ N is formed on the outer peripheral sliding surface in the same manner as the porous layer in the above embodiment. A layer having a thickness of 20 μm was formed as a hard coating. Table 1 below shows the method of nitriding treatment in each comparative example, the actually measured value of the thickness of the formed nitride layer of HV700 or more, and the length y of the chamfered portion. In Comparative Examples 3 to 6, the nitride layer contact area length x of HV700 or more cannot be specified because the nitride layer of HV700 or more is formed in the lower layer of the hard coating on the outer peripheral sliding surface. .

[Fracture resistance test]
A breakage resistance test was performed on the piston rings manufactured in the above examples and comparative examples. For the breakage resistance test, the piston ring performance evaluation apparatus according to the first embodiment disclosed in FIG. 1 of Japanese Patent Application Laid-Open No. 2001-208650, which has a pressing jig that contacts and deforms the piston ring, is used. It was. At this time, the pressing portion of the performance evaluation device uses a taper-shaped taper surface (taper angle: 7.5 °), and the reciprocating motion of the pressing jig until the piston ring breaks. Was measured. The test was performed by reciprocating the push jig so that the displacement of the load applied by the push jig of the performance evaluation device was a sine wave of 30 Hz. The piston ring breakage was detected by flowing 9.8 MPa of air through the part sealed by the piston ring, recording the air pressure change in the sealed part on the recorder, and stopping the test machine when the pressure change occurred. .

  Table 1 below shows the results of the breakage resistance test. In addition, the fracture resistance index in the following Table 1 is a value indicating the fracture resistance by indexing the fatigue strength of each piston ring when the fatigue strength of the piston ring of Comparative Example 1 is 100.

  From the said Table 1, it turns out that the piston rings of Examples 1-14 are excellent in breakage resistance. The piston rings of Comparative Examples 1 and 3 to 6 were inferior to the above examples in terms of breakage resistance. Moreover, about the piston ring of the comparative example 2, although favorable fracture resistance was obtained, the nitride layer contact area | region more than HV700 was not formed uniformly.

It is a schematic sectional drawing which shows an example of the piston ring for internal combustion engines of this invention. It is a schematic sectional drawing which shows an example of the chamfering part of the piston ring for internal combustion engines of this invention. It is a schematic sectional drawing which shows the edge part of the outer peripheral sliding surface of the piston ring for internal combustion engines manufactured with the conventional manufacturing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piston ring for internal combustion engines 2 ... Base material 3 ... Outer peripheral sliding surface 4 ... Dense layer 5 ... Porous layer 6 ... Hard film 7 ... Upper surface 8 ... Lower surface 9 ... Inner peripheral surface 10 ... HV700 or more nitrided layer 11 ... Chamfer 12 ... Nitride layer contact region of HV700 or higher

Claims (2)

A piston ring for an internal combustion engine that is mounted in a ring groove of a piston and slides with a cylinder liner or a cylinder bore,
The piston ring has an outer peripheral sliding surface, an upper and lower surface, and an inner peripheral surface, and a nitride layer is formed only on the upper and lower surfaces or only on the upper and lower surfaces and the inner peripheral surface, and ion plating is performed on the outer peripheral sliding surface. A hard film is formed by the method,
Pistons in a nitride layer contact region having a Vickers hardness (HV) of 700 or more, in which a nitride layer having a Vickers hardness (HV) of 700 or more in the nitride layer formed on the upper surface and the lower surface is in contact with the hard coating The length (x) in the ring axial direction is in the range of 3 to 40% of the length (y) in the piston ring axial direction of the chamfered portions located at the upper and lower ends of the outer peripheral sliding surface ,
The internal length of the nitride layer contact region in the piston ring axial direction (x) is in the range of 16.4 to 44.4% of the thickness (z) of the nitride layer of HV700 or more. Piston ring for engine. 2. The piston ring for an internal combustion engine according to claim 1, wherein a thickness of the nitride layer having a Vickers hardness (HV) of 700 or more is in a range of 15 to 80 μm.

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