JPH07310588A - Piston for internal combustion engine and its manufacture - Google Patents

Abstract

PURPOSE:To improve abrasion resistance and adhesion resistance on a piston ring groove surface while lowering production costs. CONSTITUTION:Plural piston ring grooves 4 are formed in the outer circumference of a piston main body 1 made of an aluminum alloy. In the piston ring groove 4, at least in a position corresponding to a top ring groove 4, an abrasion resistant ring 11, which is made of an aluminum alloy material 11b containing silicon carbide (SiC) particles 11a, is inserted, while an alumite processed layer 20 processed by anodizing is formed on the surface of the ring groove formed of the abrasion resistant ring 11, and the SiC particles 20a depositing from the abrasion resistant ring 11 are included in the inside of the alumite processed layer 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in pistons for internal combustion engines such as automobiles.

[0002]

2. Description of the Related Art As is well known, in recent years, pistons for internal combustion engines for automobiles are formed of aluminum alloy instead of cast iron in order to reduce weight in response to demand for higher output and higher performance. A plurality of piston ring grooves, in which the piston rings are mounted, are formed on the outer peripheral surface facing the inner wall surface of the cylinder bore. Further, among the piston ring grooves, the top ring groove closest to the combustion chamber is particularly exposed to a high temperature and directly receives the combustion pressure, so that the piston ring (top ring) is greatly worn. Therefore, aluminum adhesion easily occurs between the top ring groove and the top ring.

Therefore, various techniques for preventing such aluminum adhesion have been developed. For example, (1) a method in which an inorganic fiber aggregate is compounded on the surface portion of the top ring groove to strengthen it (Japanese Patent Laid-Open No. 59-59-59). (201953), and (2) In-
Application of hybrid MMC (metal matrix composite material) by Situ process to piston (Automotive Technology 198)
9-5. No. 891056), and (3) a porous nickel body is compounded on the surface portion of the top ring groove to strengthen it (Japanese Patent Publication No. 30708/1990). Also, (4)
The surface portion of the top ring groove is strengthened by an alumite treatment layer (JP-A-1-190951), or (5) an alloy layer is formed on the surface portion of the top ring groove by melting and diffusing copper or the like with an electron beam. Things (Mitsubishi Motors 19
88, NO1 "Technical Review"), and (6) Niresist cast iron in the top ring groove is subjected to Alfin treatment and cast around aluminum alloy to form a ring support member, and (7) Low Si aluminum. −
Many improved techniques have been proposed, such as casting a magnesium-based alloy member and subjecting it to alumite treatment (JP-A-1-190951).

[0004]

However, each of the conventional examples described above has the following drawbacks. That is, (1),
In the conventional examples of (2) and (3), the high pressure solidification method must be used as the forming method in view of the material such as the inorganic fiber material. Therefore, not only is the manufacturing cost increased, but the shape of the piston is restricted.

Further, in the conventional example of (4), although the alumite-treated layer improves the adhesion resistance to the piston ring, it merely forms the alumite-treated layer, so that the wear resistance is unsatisfactory. Will be enough. Further, in the conventional example of (5), on the contrary, the adhesion resistance may be insufficient.

Further, the conventional example of (6) is the technology that has been used for the longest time, and although it is possible to secure wear resistance and adhesion resistance, since it is made of cast iron, the weight must be increased. .

Further, the conventional example of (7) is aluminum-
Since a magnesium alloy wrought material is used, wear resistance and adhesion resistance are insufficient in this case as well.

[0008]

The present invention has been devised in view of the actual situation in each of the above-mentioned conventional examples. Silicon carbide (S
iC) A wear-resistant ring of aluminum alloy containing particles is cast at a position corresponding to the top ring groove of the piston made of aluminum alloy, and the surface of the ring groove formed by the wear-resistant ring is anodized (alumite treated). The feature is that an alumite treatment layer is formed.

[0009]

According to the present invention having the above-mentioned structure, the wear-resistant ring itself can be formed by casting or the like from the viewpoint of the material, and the wear-resistant ring is simply cast around during the piston molding, so that the manufacturing cost is low. Can be realized.

Further, in the present invention, silicon carbide (SiC) is dispersed in an aluminum alloy as a wear resistant ring. In particular, for example, at least the upper and lower surfaces of the top ring groove on which the alumite treatment layer is formed, the SiC deposited from the wear ring on the surface of the alumite treatment layer.
The particles are dispersed and exposed.

Since the alumite treatment layer is hard by itself and is a non-metal layer, adhesion is unlikely to occur on the piston ring which is a mating material, and therefore the alumite treatment layer is formed on the upper and lower surfaces of the top ring groove. The abrasion resistance and the scuffing resistance are improved to some extent just by forming them, but this is not always sufficient. That is, if the alumite treatment layer itself is abraded and the base material is exposed, scuffing and abrasion will rapidly progress. Therefore, in the present invention, an alloy in which SiC particles are dispersed in an aluminum alloy is used as a wear ring to disperse and expose extremely hard SiC particles of about H _V 3000 deposited from the wear ring on the surface of the alumite-treated layer, and to expose the hard particles. The SiC particles support the load from the mating material to prevent the wear of the alumite treatment layer from progressing. That is, the alumite treatment layer and SiC
Wear resistance of top ring groove due to synergistic effect with particles,
It became possible to remarkably improve the adhesion resistance.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

1 and 2 are sectional views of a piston according to the present invention, in which the piston body 1 is made of aluminum alloy (JISAC8A-T6) and is formed into a substantially cylindrical shape.
The crown portion 2 facing the combustion chamber, the three piston ring grooves 4, 5, 6 formed on the outer peripheral surface of the ring land portion 3 provided at the lower portion of the crown portion 2, the respective top, second and oil ring grooves 4 1 to 6, piston rings 7, 8 and 9 are fitted, and a skirt portion 10 below each of the ring grooves 4 to 6 is provided.

The top ring groove 4 is formed with a width of 4 mm and a depth of 8 mm around a position 9 mm away from the top surface of the crown portion 2, and only this surface portion is formed by a forming method described later. It is formed by the wear resistant ring 11.

As shown in FIG. 3, the wear-resistant ring 11 is made of an aluminum alloy 11b containing particles 11a of silicon carbide (SiC) and constitutes the surface portion of the top ring groove 4 in the piston body 1. It is cast around as much as possible.

An anodized layer 20 is formed on the surface of the wear resistant ring 11 and the outer peripheral surface of the crown 2 and ring land 3 of the piston body 1 near the top ring groove 4 by anodization. This alumite treatment layer 20 is
Particles 20a of silicon carbide SiC as in the wear resistant ring 11
Is included. That is, as described above, during the anodizing treatment, the SiC particles in the wear ring 11 are projected and contained in the alumite treatment layer 20.

Hereinafter, a specific method for manufacturing the wear resistant ring 11 will be described. That is, first, an aluminum alloy cast ingot containing 10 to 20% of SiC particles having a maximum diameter of several μm to several tens of μm was melted in an inert atmosphere such as argon gas and held at 993K, and then mechanical stirring was performed. The SiC particles are uniformly dispersed in the aluminum alloy material.

Then, in the lower mold 12 shown in FIG.
The molten aluminum alloy 13 containing C particles is injected and pressure is applied by the upper mold 14 to solidify. Then, after cooling,
After taking out the rough shaped material of the wear ring 11 from the lower mold 12,
The work for forming the wear resistant ring 11 is completed by cutting the hot water and machining it as necessary.

As the rough shape material of the wear resistant ring 11, it is possible to use a die casting method or a molten metal casting method in addition to the gravity casting method. Furthermore, there is a powder forging method as another method. This is done by mixing SiC particles and aluminum alloy particles, filling them in a mold, and applying pressure with an upper mold 14 for molding. Then, after heating, forging is added to increase the density. When the density does not increase, the density increases when the casting is repeated after heating again. According to this method, since the final product shape is finished, the subsequent machining is unnecessary and the workability is improved.

The wear-resistant ring 1 molded in this way
1 is fixed to the piston body 1 by casting. The preheating temperature of the wear-resistant ring 11 is 673 if one example of the conditions of this cast-molding is shown.
K, the pouring temperature of the piston body 1 is 993 K, the mold temperature is 473 K, and the chemical conversion treatment of the wear-resistant ring 11 is performed by heating a solution of PALCOL 3756 manufactured by Parkerizing Co., Ltd. to 313 K and immersing it for 60 seconds.

Here, the reason why the wear-resistant ring 11 is previously subjected to chemical conversion treatment is that in the case of an aluminum-based material, a dense oxide film is strongly formed on the surface, so that the contact interface with the molten metal is sufficiently welded. Therefore, the aluminum layer portion of the piston body 1 formed by the molten metal and the wear ring 11 of aluminum alloy are not sufficiently joined. In addition, the degree of heating of the molten metal can be increased, and the wear ring 11
Although a phenomenon of fusing is observed when the material is sufficiently preheated, the condition range is extremely narrow, and it is difficult to bond uniformly.

In particular, preheating the wear-resistant ring 11 may increase the thickness of the oxide film, making adhesion more difficult.

Therefore, if the chemical conversion treatment is performed in advance as described above, the chemical conversion treatment layer is oxidized by preheating, but the aluminum alloy material of the wear ring 11 is not oxidized, and the oxide of the chemical conversion treatment layer is also the piston body. Since the aluminum alloy of No. 1 is easily removed by the molten metal, the aluminum alloy of the piston body 1 and the aluminum alloy 11b of the wear ring 11 can be bonded with high bonding strength.

In addition to the top and bottom surfaces of the top ring groove 4 which is subject to severe wear, the alumite-treated layer 20 is formed only on the outer peripheral surfaces of the crown portion 2 and the ring land portion 3 near the top ring groove 4. The reason why it was not applied to the skirt portion is that if it is applied to this portion, the oil film will be broken and scuffing will occur easily.

The thickness of the alumite treatment layer 20 was set within the range of 10 to 50 μm based on the experimental results described later. That is, if it is less than 10 μm, sufficient abrasion resistance cannot be obtained, while if it exceeds 50 μm, the surface roughness becomes large and the processing cost becomes high.

Further, the size of the SiC particles 11a and 20a is set within the range of 3 to 40 μm. This is because, based on the experimental results described below, it is difficult to sufficiently support the load of the piston ring 7 when the thickness is less than 3 μm, and thus it is difficult to exhibit sufficient wear resistance.
If the value exceeds the above range, the surface roughness after the groove processing becomes large, so that the roughness after the alumite treatment also becomes large, and cracks are likely to occur in the alumite treatment layer 20, and there is a risk of peeling.

Hereinafter, the wear resistance and the adhesion resistance when the alumite treatment layer 20 is applied to the wear resistant ring 11 formed by the above-mentioned process, and the change in the characteristics of the machinability of the material of the wear resistant ring 11 material. The result of the experiment will be described.

First, the components of the matrix aluminum alloy are shown in the table. In this experiment, a sample manufactured by the casting method was used. The addition amount of SiC particles having a particle size of 9.3 ± 4 μm was set to 0, 5, 10, 15, 20, 25, and 30% by volume, and seven types of materials subjected to alumite treatment were evaluated.

Next, assuming that the volume ratio of the SiC particles is 10.0%, the particle diameter of the SiC particles to be added is 2, 5, 10, 2.
Evaluations were made on 6 kinds of materials of 0, 30, 40 μm which were subjected to alumite treatment. At the same time, the evaluation was also performed on the matrix aluminum alloy without addition of SiC particles and the one not subjected to the alumite treatment.

[0030]

[Table 1]

The evaluation method of wear resistance was carried out by using the apparatus shown in FIG. That is, the piston ring 7 is fixed on the rotary table 15 which is rotated by a motor (not shown), and the test piece 17 fixed to the lower end of the heater 16 is pressed against the piston ring 7 to wear it. The test piece 17 is an anti-wear ring cut out from the ring groove of the piston body 1. The test conditions such as temperature and lubrication condition in this method are assumed to be correlated with the actual piston of the engine. The evaluation was performed by the wear depth after the test.

The method for evaluating the adhesion resistance is carried out by using the apparatus shown in FIG. 6, and the top ring groove 4 of the piston body 1 is evaluated.
It was based on the acceleration test method in which the piston ring 7 was pressed against the lower surface and slid only in one direction of the arrows via the actuators 18 and 19. The evaluation is the piston ring 7 of the ring groove 4.
The ratio was the ratio of the area of adhesive wear to the sliding area. The test was the number of times of sliding until the alumite film was sufficiently removed.

The machinability was evaluated by machining a cylindrical rough material having a diameter of 70 mm under the following machining conditions, and the wear amount of the tool was 0.3.
It was evaluated by the number of processed pieces up to mm. Cutting speed: 200
m / min, depth of cut: 0.3 mm, feed: 0.0
3 mm (every 1 rotation), tool: vapor phase synthetic diamond tool (manufactured by Asahi Diamond Co., Ltd.) The above evaluation results are shown in Tables 2 and 3.

[0034]

[Table 2]

[0035]

[Table 3]

Here, the abrasion resistance refers to a ratio where the SiC particles are not added, that is, O, and the abrasion amount without the alumite treatment is 100. The smaller the value, the less wear.

The anti-adhesion property indicates the ratio of the adhered area of SiC particles without additive-anodized alumite treatment to 100.
The smaller the value, the less the adhesion.

With regard to machinability, the tool life was set to 100 when a rough material without addition of SiC particles was machined using CPX as a tool. However, the coarse material to which the SiC particles are added is processed by the vapor phase synthetic diamond tool.

As is clear from Tables 2 and 3, even when the amount of SiC particles added is 5% by volume, the wear resistance is significantly improved compared to the case where the amount of SiC particles is not added. Is constant.

When the alumite treatment is applied, the wear resistance of the alumite coating is superior to that of the aluminum alloy.
When the aluminum alloy containing C particles is subjected to the alumite treatment, the wear resistance is improved as compared with the case where the aluminum alloy is not treated.

On the other hand, the adhesion resistance also tends to be similar, and it can be seen that the adhesion resistance is remarkably improved as the amount of SiC particles added is increased without the alumite treatment. When the content is 25% by volume or more, no adhesion occurs.

It can be seen that when the alumite treatment is performed, no adhesion occurs even when the amount of SiC added is 5% by volume, and the adhesion resistance is remarkably improved.

Further, the machinability deteriorates even if the amount of SiC particles added is 5% by volume, as compared with the case where no addition is made. Furthermore, as the amount of addition increases, the workability deteriorates.
When the content is% by volume, the cutting edge of the tool is chipped and machining is impossible.

With respect to the effect of the size of the SiC particles, in the case of no alumite treatment, the wear resistance is remarkably improved when it is 5 μm or more accurately 3 μm or more. The adhesion resistance also seems to improve as the size of the particles increases, but there is no significant improvement when the volume ratio of the SiC particles is constant.

However, in the case of the alumite treatment, if the size of the SiC particles is 5 μm, more precisely 3 μm or more, the wear resistance is remarkably improved and the adhesion is not generated.

Further, the larger the size of the particles, the worse the workability, and when the particle size is 40 μm, the roughness after processing becomes worse, and the subsequent deterioration of the roughness due to the alumite treatment is remarkable.

From the above experiment, it can be seen that the optimum addition amount of SiC particles is 5% by volume to 25% by volume, preferably 10% by volume to 20% by volume.

The particle size is preferably 3 μm or more and 40 μm or less, and more preferably 20 μm or less.

In addition to the SiC particles described above, the dispersed particles may be BN, S as long as they have a hardness equal to or higher than the above.
Particles such as i ₃ n ₄ , Al ₂ O ₃ , WC, TiC, and TiB ₂ may be used.

The wear-resistant ring 11 formed of an aluminum alloy containing SiC particles as described above is cast into a piston body 1 of an aluminum alloy. A piston obtained by subjecting a piston to an alumite treatment is incorporated in an internal combustion engine. The test was conducted. Here, the amount of SiC particles added to the wear resistant ring 11 was set to 10% by volume. For comparison, a test of a piston not subjected to alumite treatment and a piston in which the wear resistant ring as described above was not cast around the piston body was also conducted.

The operating conditions are four cylinders and a displacement of 2000c.
Oil temperature 150 degrees, cooling water temperature 1 using diesel engine of c
Continuous operation was performed at 20 degrees for 200 hours.

As a result, the piston, which does not encircle the wear-resistant ring, is worn by 50 μm, and the wear on the lower surface of the top ring groove becomes 85.
%, While the occurrence of adhesion was observed, the wear-resistant ring 11
With a piston that has been cast around and is not anodized, wear of 5 μm occurs and 50% of the bottom surface of the top ring groove
Although the occurrence of adhesion was observed in the specimens, neither wear nor adhesion was observed in the one treated with alumite.

[0053]

As is apparent from the above description, according to the present invention, an aluminum alloy material containing silicon carbide (SiC) particles is provided with a wear ring, and a piston body made of aluminum alloy is cast to form a ring groove. Since it is formed, not only the wear resistance with the piston ring is improved, but also it can be formed by a simple molten metal casting method, so that the manufacturing cost can be reduced.

In particular, since the alumite-treated layer is formed on the ring groove surface of the wear-resistant ring, the wear resistance and anti-adhesion property of the ring groove surface are produced by the synergistic effect of the alumite-treated layer and the silicon carbide particles in the alumite-treated layer. Significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a piston showing an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of a piston of this embodiment.

FIG. 3 is an enlarged cross-sectional view of a main part of the piston of this embodiment.

FIG. 4 is an explanatory view showing die molding of the wear resistant ring of the present embodiment.

FIG. 5 is an explanatory diagram showing a wear resistance test state.

FIG. 6 is an explanatory diagram showing a test state of adhesion resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piston main body 2 ... Crown part 3 ... Ring land part 4 ... Top ring groove 7 ... Top ring 11 ... Wear resistant ring 11a ... SiC particles 20 ... Alumite treatment layer

Claims (2)

[Claims] 1. A piston of an internal combustion engine having a plurality of piston ring grooves formed on an outer circumference of a piston body made of an aluminum alloy, wherein particles of silicon carbide are present at a position corresponding to at least the top ring groove of the piston ring groove. A piston for an internal combustion engine, comprising: forming a wear-resistant ring of an aluminum alloy material containing aluminum and forming an alumite treatment layer by anodizing on the surface of a ring groove formed by the wear-resistant ring. 2. A method of manufacturing a piston for an internal combustion engine, comprising a piston body made of an aluminum alloy, and a plurality of piston ring grooves formed on the outer periphery of the piston body, wherein the wear-resistant ring containing silicon carbide is formed inside the aluminum alloy material. With pre-molding, when casting the piston body,
In the internal combustion engine, the wear ring is cast into a position corresponding to at least the top ring groove of the piston ring groove, and then the surface of the ring groove formed by the wear ring is anodized. Piston manufacturing method.