JP2000097339A - Combination of piston ring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide combination of piston rings to be well suitable for an internal combustion engine, inexpensive and have wear resistance. SOLUTION: A piston ring made of a low Cr steel containing 0.4-0.8 wt.% C and 5-11 wt.% Cr and forming an nitride layer having a white layer formed at least on a slide surface forms a second pressure ring. A first pressure ring forms a piston ring made of a stainless steel and having at least a slide surface from which a diffusion layer is exposed. Further, the thickness of the white layer is preferably 1-20 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combination of piston rings for an internal combustion engine, and more particularly to a combination of piston rings having both wear resistance and economy.

[0002]

2. Description of the Related Art Recent internal combustion engines have been aiming for higher output,
In addition, development efforts are being made to reduce weight and improve fuel efficiency and to further satisfy exhaust gas regulations. In accordance with the development trend of such an internal combustion engine, the piston ring used has been made as thin as possible in terms of shape and the material has been improved from cast iron to stainless steel. Furthermore, the corrosive atmosphere in the cylinder is deteriorated due to exhaust gas regulations, and the wear of the piston ring is intensified.

Conventionally, a cast iron ring having a sliding surface coated with hard Cr has been used as the first pressure ring of a large diesel engine.
Since plating has insufficient wear resistance, the first pressure ring is made of martensitic stainless steel, and its surface is subjected to nitriding treatment to improve wear resistance. On the other hand, the use environment of the second pressure ring is not as severe as that of the first pressure ring, and it has a complicated shape such as a tapered shape, a tapered undercut shape, and a tapered underhook. In order to further improve abrasion resistance, a chrome-plated ring including the outer periphery and the upper and lower surfaces is often used.

However, when the thickness of the second pressure ring is reduced in order to improve fuel economy, the strength of cast iron rings is insufficient. For example, Japanese Patent Publication No. 58-25863, Japanese Patent Publication No. 61-541.
No. 03 proposes that the second pressure ring is also made of the same steel material as the first pressure ring. However, there is a problem that it is economically disadvantageous to manufacture a second pressure ring whose use environment is less severe than that of the first pressure ring from the same steel material as the first pressure ring which requires high wear resistance.

To cope with such a problem, Japanese Patent Application Laid-Open No. H5-248540 discloses that the first pressure ring is composed of 11.0 to 19.0 wt% Cr.
Stainless steel with high hardness (Hv 105
The second pressure ring is made of low Cr steel containing 2.0 to 10.0 wt% and has a low hardness (less than Hv 1050) nitrided layer formed on the outer peripheral surface. Combinations of piston rings as rings have been proposed.

Japanese Patent Application Laid-Open No. 9-60726 discloses that the first pressure ring is made of martensite steel containing 15.0 to 23.0 wt% Cr and has a nitrided layer having a surface hardness of Hv 1050 or less on the outer peripheral surface. The second pressure ring should be 5.0 to 11.0
A piston made of martensitic steel containing Cr containing wt% and having a nitrided layer with a surface hardness of Hv 1040 or more formed on the outer peripheral surface, and a difference in surface hardness between the nitrided layers of both rings is Hv300 or less. Ring combinations have been proposed.

[0007]

The technique described in Japanese Patent Application Laid-Open Nos. Hei 5-248540 and Hei 9-60726 disclose the first technique.
The nitride layer formed on the outer peripheral surface of the pressure ring and the second pressure ring both removes a white layer or the like formed on the surface layer and exposes a diffusion layer in which nitrogen is diffused to the surface. The removal of the white layer is intended to prevent the hard and brittle white layer from chipping off and causing abrasive wear.

However, removing a white layer on the surface with a piston ring having a complicated sliding surface shape requires a complicated processing method and a great amount of processing time, and reduces the productivity and economy of the piston ring. There was a problem that. An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a combination of a piston ring for an internal combustion engine having both economy and wear resistance.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors have studied in more detail the working environment of a piston ring for a diesel engine. as a result,
It was confirmed that the use environment of the second pressure ring was lower gas pressure, lower heat load, and lighter lubrication conditions than the first pressure ring. Then, the present inventors, the second
The pressure ring does not necessarily need to be made of the same material as the first pressure ring, and it has been conceived that in this use environment, there is no chipping of the white layer of the nitride layer. And it was found that the depth of the nitride layer can be reduced by effectively utilizing the white layer having high hardness and high wear resistance.

[0010] The present inventors investigated the effect of the nitride layer on the wear resistance of the white layer to determine the wear amount of the piston ring and the presence or absence of the white layer of the nitride layer for the second pressure ring for a diesel engine. The relationship was investigated with a real engine. The engine used was an in-line four-cylinder diesel engine with a bore of 92 mm and a total displacement of 2400 cc. The test conditions were continuous high-speed operation of 4000 rpm × full load × 300 hr (a).
And 4000rpm × full load × 100hr−4400rpm × full load × 10
Mode endurance operation (b) of 0 hr-4000 rpm x full load x 100 hr was performed. The result is shown in FIG.

From FIG. 1, it can be seen that, when the white layer of the nitrided layer is left, the amount of wear on the sliding surface is small and no problems such as chipping occur, regardless of the test conditions. The present invention has been completed based on the above findings. That is, in the present invention, the first pressure ring is made of steel, and has a nitrided layer in which the diffusion layer is exposed at least on the sliding surface.
A combination of a piston ring, which is made of steel and has a nitrided layer including a white layer and a diffusion layer on at least a sliding surface.

Further, according to the present invention, the first pressure ring is made of martensitic stainless steel containing 0.4 to 1.2% by weight of C and 11 to 18% by weight of Cr, and the first pressure ring is diffused at least on the sliding surface. A second pressure ring comprising, by weight percent, a Cr-containing steel containing 0.4% to 0.8% C: 5% to 11% Cr and a white layer at least on the sliding surface; And a nitride layer comprising a diffusion layer and a diffusion layer. In the present invention, it is desirable that the thickness of the white layer is 1 to 20 μm.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The combination of piston rings to which the present invention is directed is composed of a combination of a first pressure ring and a second pressure ring, and is further combined with an oil ring.
In the piston ring combination of the present invention, each piston ring is preferably made of a wire and has a nitrided layer formed on at least the sliding surface. The method for forming the nitrided layer is not particularly limited in the present invention, but a nitriding treatment such as gas nitriding, ion nitriding, or salt bath nitriding is preferable. In particular, gas nitriding in an ammonia gas atmosphere or a mixed gas atmosphere of ammonia gas and nitrogen gas is preferable. It goes without saying that a nitride layer may be formed on all surfaces other than the sliding surface of the piston ring.

In the nitride layer, nitrogen diffuses inside, and a compound layer called a white layer which looks white under an optical microscope is formed on the surface. Further, a diffusion layer having a reduced nitrogen concentration is formed below the white layer (compound layer). This white layer (compound layer) is hard and rich in abrasion resistance but is brittle and chipped off during use, so it was conventionally removed before use,
In the present invention, it is actively used. In the piston ring used for the second pressure ring, a white layer is not removed in order to enhance abrasion resistance, and a ring in which a nitride layer including a white layer (compound layer) and a diffusion layer is formed on at least a sliding surface. .

The thickness of the nitrided layer, including the white layer, is 30 to 110 μm.
m is preferred. In the present invention, unless otherwise noted, the thickness of the nitride layer is a thickness including the white layer and the diffusion layer. If it is less than 30 μm, the effect is small, and if it exceeds 110 μm, it is easy to peel off. The thickness of the white layer is desirably 1 to 20 μm. If the thickness of the white layer is less than 1 μm, the thickness of the diffusion layer becomes small, and the desired thickness of the wear-resistant layer cannot be obtained. On the other hand, if it exceeds 20 μm, it is easy to peel off, which causes abnormal wear.

The hardness of the nitrided layer can be adjusted by adjusting nitriding conditions, for example, in the case of gas nitriding, the components of the atmosphere, the processing time, the processing temperature, and the like. The surface hardness of the nitrided layer is desirably set to Hv800 to 1300. If the hardness is less than Hv 800, the abrasion resistance decreases, while if it exceeds Hv 1300,
Increases opponent aggression. On the other hand, in the first pressure ring, since the use environment is severe, a brittle white layer is removed and a nitride layer exposing the diffusion layer is formed. Since the shape of the first pressure ring is relatively simple, the removal processing is simple and the diffusion layer can be easily exposed. The thickness of the nitride layer exposing the diffusion layer is preferably 50 to 110 μm. If it is less than 50 μm, the effect of improving the wear resistance is small, and if it exceeds 110 μm, it is easy to peel. The surface hardness of the nitride layer exposing the diffusion layer is desirably Hv 900 to 1400. Hardness is Hv 900
Below Hv, abrasion resistance decreases, while above Hv1400, aggression to the opponent increases.

Next, the base material of the piston ring for forming the nitride layer will be described. The piston ring of the present invention is made of steel, and is preferably made of steel containing Cr. The base material of the piston ring for the second pressure ring contains C: 0.4 to 0.8% and Cr: 5 to 11% by weight, more preferably Si: 0.1 to 0.4%, and Mn: 0.2 to 0.2%.
A steel material containing 0.4%, with the balance being Fe and unavoidable impurities. The oil ring may be made of steel having a similar composition.

C is an important element for improving the hardness and strength of the base material, and combines with Cr to form fine and hard chromium carbide, thereby improving the wear resistance of the base material. Such an effect
It is recognized at a content of 0.4% or more. On the other hand, when the content exceeds 0.8%, coarse primary carbides are easily formed, the ring becomes brittle, the strength is reduced, and the opponent aggressiveness is increased.
Increases wear on the inner peripheral surface of the cylinder. For these reasons, C is limited to the range of 0.4 to 0.8%.

Cr is an element which forms a fine chromium carbide by forming a fine chromium carbide by combining with C to form a fine chromium carbide by dissolving in the matrix to improve heat resistance and corrosion resistance, and to improve seizure resistance, wear resistance and sag resistance. Such an effect is recognized when the content is 5% or more. On the other hand, 11
%, The wear resistance is further improved, but from the usage environment, not the optimum amount of alloy addition, but excessive properties are imparted, which is economically disadvantageous, and the precipitation of chromium carbide increases, Workability deteriorates. For this reason, Cr
Was limited to the range of 5-11%.

[0020] Si is an element that acts as a deoxidizing agent and further improves sag resistance. Such an effect is 0.1
%. On the other hand, when the content exceeds 0.4%, workability is reduced and toughness is also reduced. For this reason, Si was limited to the range of 0.1 to 0.4%. Mn is an element that acts as a deoxidizing agent, increases strength, and improves hot workability. Such an effect is 0.2%
The above content is recognized. On the other hand, if the content exceeds 0.4%, the cold workability during ring forming is reduced. For this reason, Mn
Was limited to the range of 0.2 to 0.4%.

The balance consists of Fe and inevitable impurities. As inevitable impurities, P: 0.04% or less,
S: 0.03% or less is allowable. Further, the first pressure ring is preferably made of a base material having the following composition. The first pressure ring for the diesel engine has heat resistance in addition to wear resistance.
Scuff resistance is required. Therefore, the first pressure ring contains a martensitic stainless steel having a high Cr content, that is, C: 0.4 to 1.2% and Cr: 11 to 18% by weight, and more preferably Si: 0.2 to 18%. 0.5%, Mn: 0.2
~ 0.5% or further Ni: 0.6% or less, M
o: Martensitic stainless steel material containing at least one of 1.25% or less and V: 0.15% or less, the balance being Fe and unavoidable impurities (for example, SUS410J1,
440B) is preferably applied.

If C is less than 0.4%, the amount of carbides contributing to abrasion resistance is insufficient, so that excellent abrasion resistance cannot be obtained. on the other hand,
If C exceeds 1.2%, the carbides become coarse and the strength is insufficient. For this reason, C is desirably limited to the range of 0.4 to 1.2%. Cr forms a solid solution to improve corrosion resistance and heat resistance, and also forms carbides to contribute to improvement of wear resistance. However, if less than 11%, these effects are small, while 18%
If the content exceeds 2, the amount of Cr dissolved in the matrix increases, and the corrosion resistance improves, but the strength increases and the toughness deteriorates. Therefore, it is desirable to limit Cr to 11 to 18%.

Si is an element that acts as a deoxidizing agent and further improves sag resistance. Such an effect is 0.2
%. On the other hand, if the content exceeds 0.5%, workability is reduced and toughness is also reduced. For this reason, Si is preferably limited to the range of 0.2 to 0.5%. Mn is an element that acts as a deoxidizing agent, increases strength, and improves hot workability. Such an effect is observed at a content of 0.2% or more. On the other hand, 0.5%
If the content exceeds 2, the cold workability during ring forming is reduced. For this reason, Mn is preferably limited to the range of 0.2 to 0.5%.

In addition, one or more of Ni: 0.6% or less, Mo: 1.25% or less, and V: 0.15% or less may be added for the purpose of improving wear resistance and heat resistance. The balance consists of Fe and inevitable impurities. As unavoidable impurities,
P: 0.04% or less, S: 0.03% or less are allowed. The piston ring of the present invention is desirably manufactured by processing a steel material obtained by melting a steel having the above-described composition from a material that is formed into a wire by hot rolling or the like, and performing an appropriate heat treatment as necessary. Further, instead of production from molten steel, a sintered alloy may be used.

FIG. 2 shows a combination of a piston ring for a diesel engine according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing a state in which a piston is mounted in the bore of the cylinder. A piston 2 is inserted into a bore in a cylinder 1, and a first pressure ring 6, a second pressure ring 7, and a combined oil ring 8 are provided in piston ring grooves 3, 4, 5 formed on an outer peripheral surface of the piston 2. Each is attached.

Although the first pressure ring 6 shown in FIG. 2 is a single-sided keystone type ring, it is not limited to this shape, and may be a double-sided keystone type or rectangular. On the sliding surface of the first pressure ring 6 and other outer surfaces, a nitride layer 10 having an exposed diffusion layer is formed. Also,
Although the second pressure ring 7 in FIG. 2 is a taper face type ring, it is required to have a shape such as a taper undercut, a taper inner cut, or the like, since the lubricating oil is required to be scraped together with airtightness. Needless to say. A nitride layer 9 having a white layer is formed on the sliding surface and other outer surfaces of the second pressure ring 7. FIG.
Oil ring 8 is an oil ring with a coil expander 11 and has an almost I-shaped cross section.
A nitride layer 9 is formed on the outer peripheral surface of the substrate 12.

[0027]

EXAMPLE A first pressure ring and a second pressure ring having the shapes shown in FIG. 1 were produced using the stainless steel materials shown in Table 1. Table 3 shows these rings in the diesel engine.
They were mounted in combinations as shown in (a) and (b), and an actual machine test was performed. After the test, the wear amount of the piston ring sliding surface was examined.

The test engine is an in-line 4-cylinder, bore inner diameter:
The model uses a diesel engine with a displacement of 92 mm and a total displacement of 2400 cc, and performs continuous high-speed operation and mode endurance operation. The test conditions for continuous high-speed operation were 4000 rpm x full load x 300 hr, and the test conditions for mode endurance operation were 4000 rpm x full load x 100 hr-4400
rpm x full load x 100 hr-4000 rpm x full load x 100 hr. The engine oil used was 10W-30.

The dimensions of each piston ring are as follows: width of the first pressure ring: 2.0 mm × thickness of 3.35 mm, width of the second pressure ring:
It was 1.5 mm x 3.30 mm thick. Table 2 shows the nitriding conditions of each piston ring, the hardness of the outer peripheral surface, and the thickness of the nitride layer including the white layer and the white layer. The thickness of the nitride layer of the first pressure ring is the thickness of the nitride layer where the diffusion layer from which the white layer has been removed is exposed.

Table 3 shows the results of the actual machine test. The amount of wear of the piston ring was represented by the amount of decrease in thickness at the sliding position.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

The combination of the piston rings of the present invention results in a piston ring having sufficient wear resistance for use in diesel engines. The second example in which the diffusion layer is exposed as a comparative example
Compared with the pressure ring, the abrasion resistance is improved, and no trouble such as chipping occurs.

[0035]

According to the present invention, it is possible to provide an inexpensive piston ring which satisfies the required abrasion resistance without requiring the processing of removing the white layer of the nitride layer, and is industrially remarkable. Has the effect of In addition, there is an effect that the depth of the nitrided layer can be reduced, which is economical.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the presence or absence of a white nitride layer on the amount of wear of a piston ring in an actual engine. (A) shows the case of the continuous high-speed condition, and (b) shows the case of the mode endurance condition.

FIG. 2 is a longitudinal sectional view showing one example of a combination of piston rings.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Piston ring groove 4 Piston ring groove 5 Piston ring groove 6 First pressure ring 7 Second pressure ring 8 Combined oil ring 9 Nitride layer 10 Surface hardened layer 11 Coil expander 12 Oil ring

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Kawashima 5-2-6, Honcho Nishi, Yono-shi, Saitama Japan Piston Ring Co., Ltd. Yono Plant F-term (reference) 3J044 AA02 AA18 BA03 BB06 CB13 CB15 CB20 DA09 DA16

Claims (3)

[Claims] The first pressure ring is made of steel and has a nitrided layer having a diffusion layer exposed on at least a sliding surface, and the second pressure ring is made of steel and has a white layer and a diffusion layer on at least a sliding surface. A combination of piston rings, characterized by having a nitrided layer comprising: 2. The method according to claim 1, wherein the first pressure ring has a C: 0.4% by weight.
And a nitride layer having a diffusion layer exposed at least on a sliding surface, and the second pressure ring has a weight% of
A piston ring comprising a Cr-containing steel containing C: 0.4 to 0.8% and Cr: 5 to 11%, and having at least a nitrided layer comprising a white layer and a diffusion layer on a sliding surface. combination. 3. The piston ring combination according to claim 1, wherein the thickness of the white layer is 1 to 20 μm.