JPH09122884A - Production of piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve strength and to prevent a failure, etc., by decreasing the volumetric rate of the carbon short fibers on a surface part while assuring the wear resistance and coagulation resistance of a composite member. SOLUTION: This process for producing a piston comprises forming the inner peripheral wall of the top ring groove of a piston body of the composite member 11 formed by combining the carbon short fibers 13 and potassium titanate whiskers 14 with an aluminum alloy material and mixing the carbon short fibers 13 at a ratio of 30 to 60% (vol.%) with the entire part of the composite member 11. A perform body 15 consisting of the carbon shot fibers 13 and the potassium titanate whiskers 14 is previously molded and the molding is heated at about 400 to 550 deg.C in the atm. to burn the carbon short fibers of the surface part Z.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine of, for example, an automobile, particularly an internal combustion engine in which the inner wall of a piston ring groove is formed of a composite member made of aluminum alloy material and short carbon fibers and potassium titanate whiskers. The present invention relates to a method for manufacturing a piston.

[0002]

2. Description of the Related Art As a conventional piston for an internal combustion engine of this type, there is one described in Japanese Patent Application No. 6-29880 filed by the present applicant.

The piston body is formed of an aluminum alloy into a cylindrical shape with a lid, and three piston rings are formed on the crown portion facing the combustion chamber and the outer peripheral surface of the ring land portion below the crown portion. It has a groove.

The top ring groove of the piston ring groove is formed by a composite member having an annular surface, and the composite member 30 is made of aluminum or aluminum as a base material as shown in FIGS. 8A and 8B. An alloy material (C8A, A390, etc.) 31 containing carbon short fibers 32 and potassium titanate whiskers (K ₂ O · 6TIO ₂ ) 33 is used as a composite part material and is formed into an annular shape.
It is surrounded by casting 9 to form the surface portion of the top ring groove.

That is, in the composite member 30, the short carbon fibers 32 are blended in a proportion of 30 to 60% by volume with respect to the whole composite member, and the potassium titanate whiskers 33 are contained in the short carbon fibers 32 in an amount of 20 to 50% by volume. It is blended in the ratio of%. The total amount of the short carbon fibers 32 and the potassium titanate whiskers 33 is set to 60% by volume or less of the entire composite member 30.

Accordingly, the wear resistance of the inner peripheral surface of the top ring groove against sliding contact with the piston ring (top ring) is improved, and the adhesion resistance to the piston ring due to the self-lubricating action of the carbon short fibers 32 is improved. To do. Further, the potassium titanate whiskers 33 have various advantages such as further improved wear resistance.

[0007]

However, in the conventional example according to the prior application, as described above, the short carbon fiber 3 is used.
Since 30% by volume of 2 is mixed in the entire composite member 30, the abrasion resistance of the composite member 30 is improved, but the carbon short fibers 32 having a large volume ratio are uniformly dispersed inside the composite member 30. As a result, sufficient strength may not be obtained and weakening may occur. Therefore, when the composite member 30 is processed by cutting or the like, it may be damaged or peeled off.

When the composite member 30 is cast during casting of the piston body 29, as shown in FIG. 8C, at the interface 34 between the piston body 29 and the composite member 30, particularly at the end face of the top ring groove, the piston is Cracks may occur due to high heat load during actual operation.

[0009]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned conventional circumstances, and a plurality of piston ring grooves are formed on the outer circumference of a piston body made of an aluminum alloy material, and the piston ring is formed. At least the inner peripheral wall of the top ring groove of the groove is formed of a composite member in which short carbon fibers and potassium titanate whiskers are combined, and the short carbon fibers account for 30 to 60% (volume%) of the whole composite member. In the method for producing a piston for an internal combustion engine, which is compounded in a proportion, the composite member is preliminarily molded into an annular molded body composed of short carbon fibers and potassium titanate whiskers, and the molded body is placed in an oxidizing atmosphere. It is heated under a condition of a predetermined heating temperature and heating time, and then the molten aluminum alloy material is impregnated with the molded body at the time of molding the piston main body to form the piston body. When it is characterized in that integrally molded.

As described above, by heating the molded body of the composite member before integrally molding with the piston body, a part of the carbon short fibers on the surface of the molded body is burned and burned off, and The volume ratio of short carbon fibers can be reduced.

[0011]

1 and 2 are sectional views of a piston used in the present invention. In this piston, a piston body 1 is made of an aluminum alloy material 12 in a substantially cylindrical shape and faces a combustion chamber. Three piston ring grooves 4, which are formed on the outer peripheral surface of the crown portion 2 and the ring land portion 3 provided at the lower portion of the crown portion 2.
5, 6 and a skirt portion 10 below each of the ring grooves 4 to 6, and piston rings 7, 8 and 9 are fitted in the top, second and oil ring grooves 4 to 6, respectively.

The top ring groove 4 has a width of 4 m centering on a position 9 mm away from the top surface of the crown portion 2 toward the skirt portion 10 side.
In addition to being formed to have a depth of m and a depth of 8 mm, only this surface portion is formed by an annular composite member 11 formed by a forming method described later.

As shown in FIGS. 5 to 7, the composite member 11 is a composite material containing short carbon fibers 13 having a length of 0.1 to 10 mm and potassium titanate whiskers (K ₂ O.6T10 ₂ ). And is cast in the piston body 1 so as to form the surface portion of the top ring groove 4.

More specifically, this composite member 11
Is formed by press forming, and the reinforcing fiber is formed as the preform body 15.
The volume ratio V _f of the short carbon fibers 13 is 55 to 60% by volume with respect to the entire composite member 11, and the potassium titanate whiskers 14 are mixed at a ratio of 20 to 50% by volume with respect to the short carbon fibers. ing. Therefore, the short carbon fiber 13
The mixing ratio of the potassium titanate whiskers 14 is set to 4: 1. Further, the extent of the reinforcing fibers of the short carbon fibers 13 and the potassium titanate whiskers 14 in the composite member 11 is 60% by volume.

The amount of composite of both carbon short fiber 13 and potassium titanate whisker 14 is taken into consideration in the strength of the preform body 15, the permeability of the molten aluminum alloy (depending on the fiber density), and the performance of the composite member 11. And decided.
First, the castability of the preform body 15 having the fiber density, that is, the ratio of the reinforcing fiber to the composite member 11, that is, the volume ratio V _f of 60% or more is poor, and therefore the upper limit was made 60%. On the other hand, when the preform body 15 is pressure-cast, the volume ratio is preferably 30% or more so that the fibers are entangled in the composite member 11 to obtain a uniform dispersion. Therefore, the lower limit is 30%. . Next, the amount of potassium titanate whiskers 14 in the short carbon fibers 13 is 20% (that is, short carbon fibers: potassium titanate whiskers = 4:
In the case of 1) or less, the strength of the preform is insufficient and molding cannot be performed. On the other hand, when it exceeds 50% by volume (short carbon fibers 13: potassium titanate whiskers = 1: 1), aggregates of potassium titanate whiskers 14 are likely to be formed, which makes it difficult to form a uniform aluminum composite member. The amount of the potassium titanate whiskers 14 in the short carbon fibers 13 is preferably 20 to 50% by volume.

The base material of the aluminum alloy material 12 of the piston body 1 provides the basic strength of the composite member 11, and AC8A, 6061 and the like are aluminum alloy materials having a strong age hardening property and potassium titanate. Since it has good wettability with the whiskers 14 and the short carbon fibers 13, it is desirable as a base alloy.

Hereinafter, a specific method of manufacturing the composite member 11 will be described.

That is, first, a single fiber is a carbon short fiber 13 having a diameter of 5 to 15 μm and a length of 0.1 to 10 mm (specific gravity 1.77 g / cm 2).
³ ) and the monofilament has a diameter of 0.4 to 1.5 μm and a length of 10 to 10
0 μm potassium titanate whiskers 14 (specific gravity 3.3 g
/ Cm ³ ) in a predetermined weight ratio and put in water, and after sufficiently stirring, press molding using a die (pressure 20 kgf
/ Cm ² ) to form a cylindrical shape and dried to form a preform body 15. The preform body 15 was formed in a ring shape having an outer diameter of 86 mm, an inner diameter of 72 mm and a thickness of about 11 mm (see FIG. 3A).

Subsequently, the preform body 15 is heated in an oxidizing atmosphere, that is, in the air at about 550 ° C. for about 20 minutes, and the carbon short fibers 13 on the surface portion Z of the preform body 15 are heated.
Was burned (see FIG. 3B). As a result, in the preform body 15, as shown in FIGS. 3B and 5, the interior Y has a high volume ratio V _f of the carbon short fibers 13, but the surface portion Z is burned by the carbon short fibers 13 and has a volume ratio V _f. Is decreasing.

The preform body 15 thus molded is fixed to the piston body 1 by casting.
C). As an example of the conditions of the cast-molding, the preheating temperature of the preform body 15 is 673K, the pouring temperature of the piston body 1 is 993K, the mold temperature is 473K, and the surface of the preform body 15 is washed with an alkaline solution or an organic solvent. ， Degrease.

Then, as shown in FIG. 3D, the ring land portion 3 of the piston body 1 in which the preform body 15 is cast.
The outer periphery of the preform body 15 is cut to reduce the thickness between the outer peripheral surface of the preform body 15 and the outer surface of the ring land portion 3. Then, as shown in FIG. 1, the top ring groove 4 is finished by cutting to complete the manufacturing.

The results of experiments on the change in the volume ratio V _f of the short carbon fibers 13 when the preform body 15 is heated in the atmosphere and Ar gas at a predetermined temperature will be described below.

First, a test material 15a for the preform body 15
The ring was cut into a length of about 15 to 20 mm, and a heating test was performed in the atmosphere and Ar gas as shown in Table 1. Test conditions; At 600 ° C., heating in the atmosphere and heating in an Ar gas stream were performed at each temperature.
The flow rate of Ar gas was fixed at 15 l / min. The holding time was set to 10 minutes at intervals of up to 60 minutes.

[0024]

[Table 1]

Evaluation method: First, in order to clarify the reduced (burnt) state of the short carbon fibers, the test material 15 after the heating test was performed.
The appearance of the whole a and the cross section was observed. Next, a cross-section of the surface layer of the sample material was observed with a scanning electron microscope (hereinafter referred to as SEM), and the carbon short fiber diameter was measured with an SEM photograph (average fiber diameter 13.0 μm).

As this experimental apparatus, the one shown in FIG. 4 was used, and the quartz tube 18 was inserted and held in the tubular furnace 17 on the bases 16 and 16, and the preform body 15 was placed inside the quartz tube 18. The test pieces 15a of 1 are arranged. Further, the Ar gas in the Ar gas cylinder 19 is fed into the quartz tube 18 from one end thereof. Furthermore, the test piece 15
A thermometer 20 for detecting the temperature near a is set.

The results of this experiment are shown in Table 2.

[0028]

[Table 2]

As is clear from the results of these experiments, A
In the r gas, the fiber diameter does not change regardless of the temperature change and the holding time, but in the air, the fiber diameter decreases only in the vicinity of the surface of the test piece 15a with the holding time of 400 ° C. for 50 to 60 minutes, and , Holding time at 450 ° C for 30 to 50 minutes,
At 500 ° C., a holding time of 20 to 40 minutes, and at 550 ° C., a holding time of 10 to 30 minutes showed a decrease in fiber diameter.

Therefore, by performing the heat treatment under the above-mentioned conditions, as shown in FIG. 5, on the surface portion Z of the preform body 15, the low volume fraction region (about 20% by volume) of the carbon short fiber 13 as described above is formed. ) Occurs, and a high volume ratio region (about 5
5% by volume). And this preform body 15
When the molten aluminum alloy is infiltrated and solidified at a high pressure in FIG. 5, as is clear from FIGS. 5 to 7, in the vicinity of the interface X with the piston body 1 which is the surface portion Z, the volume ratio V _{f of the} carbon short fibers 13 is V _f. Is about 20% (see FIG. 6), whereas it is clear that the volume ratio V _f is about 55% inside the right side of the figure (see FIG. 7). Therefore, the carbon short fibers 13 from the surface portion Z to the inside Y are heated by the heat treatment.
It has become possible to easily obtain a graded material in which the volume ratio of is gradually changed.

As a result, weakening is suppressed near the interface between the composite member 11 (preform body 15) and the piston body 1, that is, near the surface portion Z, and the strength is improved.
When the top ring groove 4 is finally formed by cutting and cutting, the surface portion Z is not likely to be damaged or peeled off.

Further, after the composite member 11 is cast into the piston body 1, a large difference in mechanical properties does not occur in the vicinity of the interface between the two, so that cracking due to high heat load during actual operation of the piston occurs. Is prevented.

The higher the heating temperature of the preform 15 is, the shorter the desired temperature can be obtained. However, an appropriate temperature is selected according to the cycle time. However, 6
As shown in the above table, the desired product cannot be obtained at a heating temperature of 00 ° C. or higher.

[0034]

As is apparent from the above description, according to the present invention, the short carbon fibers are contained in the composite member in an amount of 30 to 60.
The volume ratio of the short carbon fibers on the surface part was decreased by heating the compact compounded in a volume ratio of 100% in an oxidizing atmosphere to burn the short carbon fibers on the surface part of the compact. The weakening of the surface portion near the interface between the member and the aluminum alloy base material of the piston body is suppressed, and the strength is improved.

As a result, damage or peeling of the surface portion during cutting of the composite member can be prevented.

Further, it is possible to prevent the composite member from cracking due to a high heat load when the piston is actually operated after the piston is assembled to the engine.

Since the volume fraction of the carbon short fibers inside the composite member is large, the wear resistance and the adhesion resistance of the inner peripheral surface of the ring groove to the piston ring are improved by the synergistic action with the potassium titanate whiskers. .

[Brief description of the drawings]

FIG. 1 is a sectional view of an essential part of a piston used in a manufacturing method of the present invention.

FIG. 2 is a vertical sectional view of the piston.

FIG. 3A is a cross-sectional view showing a part of a preform body. B is a cross-sectional view after the preform body is heat-treated, C is a partial cross-sectional view showing a state in which the preform body is cast into the piston body, and D is a partial cross-sectional view in which the outer periphery of the ring land portion is cut.

FIG. 4 is a schematic view of an experimental apparatus for a preform body used in the present invention.

FIG. 5 is an enlarged view showing a distribution of short carbon fibers in a cross section of the composite member used in the present invention.

6 is an enlarged view of a Z portion of FIG.

FIG. 7 is an enlarged view of a Y portion of A.

8A is a perspective view showing a conventional composite member, B is a perspective view in which a broken line portion of A is cut out, and C is an enlarged view of an E portion of B. FIG.

[Explanation of symbols]

 1 ... Piston body 4 ... Top ring groove 11 ... Composite member 12 ... Aluminum alloy material 13 ... Short carbon fiber 14 ... Potassium titanate whisker 15 ... Preform body (molded body) Z ... Surface part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuu Tomono 5-3-8 Nishikujo, Konohana-ku, Osaka City, Osaka Prefecture Hitachi Shipbuilding Co., Ltd. (72) Seiichi Kotake 5-chome, Nishikujo, Konohana-ku, Osaka, Osaka Prefecture 3-28 Hitachi Shipbuilding Co., Ltd. (72) Inventor Junichi Fujita 4-1-2 Hiranocho, Chuo-ku, Osaka City, Osaka Prefecture Osaka Gas Co., Ltd.

Claims (1)

[Claims] 1. A plurality of piston ring grooves are formed on the outer periphery of a piston body made of an aluminum alloy material,
At least the inner peripheral wall of the top ring groove of the piston ring groove is formed of a composite member in which short carbon fibers and potassium titanate whiskers are combined, and the short carbon fibers account for 30 to 60% (volume) with respect to the entire composite member. %) In the method for producing a piston for an internal combustion engine, wherein the composite member preforms an annular shaped body composed of short carbon fibers and potassium titanate whiskers and oxidizes the shaped body. It is characterized in that it is heated under a condition of a predetermined heating temperature and a heating time in an atmosphere, and thereafter, the formed body is impregnated with a molten aluminum alloy material at the time of forming the piston body and integrally formed with the piston body. Manufacturing method of piston for internal combustion engine.