JPS61294159A - Al-alloy piston for internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent the formation of crack at the port edge part of a combustion chamber by composite-reinforcing a pair of regions opposed each other in the direction of piston out of the port edge part of a recessed combustion chamber which is formed at the top surface of the captioned piston, by inorganic fiber, and applying hard alumite treatment onto the top surface. CONSTITUTION:In the application for an Al alloy piston 1 for direct injection type Diesel engine, a recessed combustion chamber 4 is formed onto the top surface 11 of the piston 1, and a composite reinforced part 9 composite- reinforced by inorganic fiber is formed in a pair of regions which exist in opposed form each other on the top surface 11 in the direction of a piston pin 3 at the port edge part 12 of the combustion chamber 4. An alumite treated part 8 having a thickness of 30-110mu is formed in all the region except the composite reinforced part 9 out of the piston top surface 11, through alumite treatment. Therefore, generation of crack at the port edge part 12 of the combustion chamber due to thermal stress and mechanical stress can be effectively suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION C. Industrial Application Field The present invention relates to an aluminum alloy piston for internal combustion engines having a concave combustion chamber on its top surface.

[Summary of the invention]

The present invention is an internal combustion aluminum alloy piston with a concave shape on its top surface and a combustion chamber.
A pair of mutually opposing regions of the mouth edge of the combustion chamber i at least in the direction of the piston pin are reinforced with inorganic fibers, and at least the top surface is preferably partially coated with hard alumite. This treatment effectively prevents cracks from forming at the mouth edge of the combustion chamber.

[Conventional technology]

A piston for an internal combustion engine having a concave combustion chamber on its top surface;
That is, the piston for a direct injection diesel engine is made of a light alloy such as an aluminum alloy because it has excellent thermal conductivity and specific gravity. In addition, Figures 3 and 4
The figure shows a conventional aluminum alloy piston 1 for an internal combustion engine having such a configuration, and FIG. , and FIG. 4 also fidgets with the formed O.

However, an aluminum alloy piston for an internal combustion engine in which a concave combustion chamber 4 is formed as shown in FIG. 3 and R11 has a high temperature. Since it operates under load, high thermal stresses occur, especially in the mouth 12 of the combustion chamber 4. On the other hand, since the piston 1 is made of an aluminum alloy, its strength against thermal stress is extremely low compared to a piston made of cast iron or the like. For this reason, the mouth edge 1 of the combustion chamber 4 of the piston 1 is caused by the thermal stress.
Cracks 7 often occur in the piston 2, and the cracks 7 reduce the durability of the piston 12 and thus of the internal combustion engine in which the piston 1 is used.

Note that the cracks 7 do not occur uniformly over the entire circumference of the mouth edge 12 of the combustion chamber 4. For example, in FIG. In the case of the piston 1 shown in FIG. 1, the cracks 7 are concentrated in a pair of first regions 13 that are present on the top surface 11 of the mouth edge 12 in a direction perpendicular to the piston pin 3 and are opposed to each other. Furthermore, in the case of the piston l shown in FIG.
The cracks 7 are concentrated in four neighboring regions 14 near the line 18 where the lines 18 and 7 intersect.

That is, in the case of the piston 1 shown in FIG. 3, compressive thermal stress generated by overheating of the mouth edge 12 of the combustion chamber 40 and combustion pressure are applied to the first region 13. Since the generated compressive stress works together with the cracks 7, the cracks 7 are concentrated in the pair of regions 13 of the mouth edge 12. Further, in the case of the piston 1 shown in FIG. 4, the area 14 near the mouth edge 12 has a complicated shape.
Since the temperature distribution in the vicinity area 14 is not uniform and thermal stress is generated as a result, the cracks 7 are concentrated in the area 4 near the mouth edge 12. In short, in the case of both the pistons shown in FIGS. 3 and 4, thermal stress generated by combustion is the main cause,
For this reason, an aluminum alloy piston 1 for an internal combustion engine has been put into practical use in which the crack 7 as described above is prevented from occurring by applying hard alumite treatment to the top surface II.

However, in the case of a piston that has been subjected to such alumite treatment, cracks 7 occur in a pair of second regions 15 that are located on the top surface 11 of the mouth edge 12 of the piston 1 and that face each other in the direction of the piston pin. It becomes easier to do.

In order to solve these problems, the special public
In Publication No. 85, when performing hard alumite treatment on the top surface, a pair of mutually opposing regions (i.e., the above-mentioned second An aluminum alloy piston for internal combustion engines that is not hard alumite-treated has been proposed in the area (1).

[Problems to be Solved by the Invention] However, even in the piston proposed in the above-mentioned Japanese Patent Publication No. 58-53185, the stress l?
Due to the 1ljIl-like variation +1, cracks may still occur in the second region, and no effective countermeasure against the occurrence of such cracks has been found.

[Means for solving problems]

The present invention was invented to solve the above-mentioned problems, and in an aluminum alloy piston for an internal combustion engine having a concave combustion chamber on the top surface, the piston has a concave combustion chamber on the top surface. A pair of mutually opposite regions present on the top surface in at least the direction of the piston pin are compositely reinforced with inorganic fibers, and at least the top surface is partially or entirely subjected to hard alumite treatment. This invention relates to an aluminum alloy piston for internal combustion engines.

〔Example〕

An embodiment in which the present invention is applied to an aluminum alloy piston for a direct injection type diesel engine will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows four pistons according to an embodiment of the present invention. In FIG. 1, a piston l made of an aluminum alloy has a pair of pin holes 10. As shown in FIG. Then, the piston pin 3 whose center portion is fitted into the connecting rod 2 is inserted with its both ends into the pin holes 10 and maintained in this inserted state, so that the piston pin 3 is connected to the piston 1. It is connected to rod 2.

Further, a concave combustion chamber 4 is formed in the top surface 11 of the piston 1 . A pair of second regions facing each other on the top surface in the direction of the piston pin of the mouth edge 12 of the combustion chamber 4 are filled with SiC whiskers having a diameter of 1μ or less and an aspect ratio of 50 or less, and alumina having a diameter of 5μ or less. No long fibers or short fibers, stainless steel long fibers with a diameter of 0.8μ or less! s, a composite reinforcement part 9 compositely reinforced with fibers is provided. In addition, before casting the piston l, inorganic u
The composite reinforced portion 9 can be easily formed in the piston 1 by arranging a fiber preform and then casting the piston 1. Further, in almost the entire remaining 9M region of the top surface 11 excluding the composite reinforced portion 9, a hard alumite treated portion 8 having a thickness of 30 to 110 μm is formed by hard alumite treatment.

As mentioned above, the present inventors discovered that the composite reinforced portion 9 as shown in FIG.
It has been found that in the case of a piston in which the hard alumite treated portion 8 is formed in a region other than the region, the a-crack 7 may occur in the second region.

After investigating such a case, the tensile stress at the mouth edge 12 of the combustion chamber 4 under the action of combustion pressure was approximately 2.5 kg.
It has been found that cracks 7 often occur under conditions exceeding "r/Tsuru". In other words, under certain conditions, the mouth edge 12 of the combustion chamber 4 is When an almost constant compressive stress due to the thermal stress caused by the high temperature on the outer part and a mechanical tensile stress that constantly fluctuates with each combustion cycle are applied, and the amplitude of this stress is large. It has been found that the cracks 7 occur due to fatigue of the material due to periodic fluctuations in stress.Therefore, in the present invention, in order to increase the fatigue strength of the piston material made of aluminum alloy under high temperatures caused by combustion, the cracks 7 are generated in the combustion chamber 4. A composite reinforcing portion 9 made of non-molecular fibers as described above was formed on the edge portion 12.

It was confirmed by a thermal shock test in which a pure thermal load was repeatedly applied that the fatigue strength was improved when such a composite reinforced portion 9 was formed.

Next, in an aluminum alloy piston in which a composite reinforcement part 9 is formed with alumina fiber (short fibers were used in this case) around the entire circumference of the mouth edge 12 of the combustion chamber 4 on the top surface 11, the four types described below are used. When we investigated the total length of cracks per piston (1 square) with respect to the volumetric filling rate (%) of alumina fiber in each case where the hard alumite treatment area 8 of the type was formed, the results shown in Fig. 2 were 11.
It was done. In this experiment, the bore diameter of the cylinder was 100-
An in-line 4-cylinder squisochelisobu direct injection diesel engine was accelerated and decelerated for 50 n (r!Tl) idling, no f (load, water temperature 40°C), full speed, 10
The test was carried out under the following conditions: % overload, water temperature of 110°C, and repeated stirring for 3 minutes each. In addition, the vertical axis of the graph in Figure 2 is the 1st value per 71 screws.
#3 length of the crack that occurs in the region or the second region of IJ (
11), and the horizontal axis indicates the volumetric filling rate (%) of alumina il and k II in the composite reinforced portion 9, respectively.

In Fig. 2, A is a crack 7 that occurs in the first region when hard alumite treatment is applied only to the first region.
B indicates the first area when hard alumite treatment is not applied to only the first area and is applied to the entire circumference of the mouth edge 12 on the top surface 11 excluding the first area. C indicates the total length of the crack 7 that occurs in the second region when hard alumite treatment is applied only to the second region, and ■) indicates the total length of the crack 7 that occurs in the 20th region only; It shows the total length of the crack 7 that occurs in the second region when hard alumite treatment is not applied to the entire periphery of the mouth edge 12 on one side of the TrI surface except for the second region.

1- The following conclusion emerged from the experimental results described above.

]) If only the first region is hard alumite treated after forming the composite reinforced portion 9, then only the first region is hard alumite treated after the composite reinforced portion 9 is formed. If no hard alumite treatment is applied to the entire circumference of the mouth edge 12 on the top surface 11 except for the first area (case B), or if the composite reinforcement part 9 is not formed and hard alumite treatment is not applied. Compared to
If it is 0% or less, the occurrence of cracks 7 in the first region tends to decrease. However, in the case of , compared to the case where the hard alumite treatment is performed only on the first region without forming the composite reinforcement part 9 (when the volume filling rate is 0%), the first region is fLL12 occurrence in the region tends to increase.

2) When hard alumite treatment is applied only to the second region without forming the composite reinforcement part 9 (body C, when the bulk filling rate is about 0%), the composite reinforcement part 9 is not formed and Compared to the case where hard alumite treatment is not performed, the occurrence of cracks 7 in the second region tends to increase significantly. On the other hand, when hard alumite treatment is performed only on the second region after forming the composite reinforced portion 9 (case C), the composite reinforced portion 9 is not formed and li5! The occurrence of cracks 7 in the second region tends to decrease when the volume filling rate is around 20%, compared to the case where no alumite treatment is performed. Also, after forming the composite reinforcement part 9, hard alumite treatment was not applied to only the second area, but the hard alumite treatment was applied to the entire circumference of the mouth edge part 12 on the top surface 11 except for the second area. In case (D), compared to case C, the occurrence of cracks 7 in the second region tends to be significantly reduced or no cracks 7 occur.

3)? , the volumetric filling rate (■) of the S1 reinforcing and stiffening fibers is within a certain range, the occurrence of cracks 7 tends to decrease.

The present inventors also found that when the volume filling rate of D in 1) above is 0%, the volume filling rate of D in 2) above is 20%.
In the case of % and in the case of to? Considering the role of the M joint reinforcement part, we came up with the piston l shown in Fig. 1.

As mentioned above, in the above experiment, hard alumite treatment was applied to the mouth edge 1 of the combustion chamber 40 on the top surface 11 of the piston 10.
It was applied to part of 2. This is because 1tL cracks 7 begin to form from the mouth edge 12, and applying hard alumite treatment to this mouth edge 12 has the greatest effect on the occurrence of the cracks 7.

Furthermore, in addition to the above-described experiment using alumina fibers shown in FIG. 2, an experiment was also conducted in which the composite reinforced portion 9 was formed with SiC whiskers. As a result of this experiment, it was found that when SiC whiskers are used, the occurrence of cracks 7 tends to be reduced compared to when alumina fibers are used.

Furthermore, when the volumetric filling rate V of SiC whiskers is as high as , the occurrence of cracks 7 is significantly reduced, that is, S
It was found that iC whiskers have a greater effect in suppressing the occurrence of turtle 27 than alumina fibers.

2 J, Unami heli 1-ka 51, SiC rice car, alumina JIIU ill and stainless steel 1jF
When forming the composite reinforcement part 9 in the step i4. The effective volume filling factor ■ to suppress is 12~
35%, 7-30% and 15-IIO%.

Here, the lower limit value of the volume filling rate V is this value IN
], upper (16) is set to a value around 1, at which the occurrence of cracks 7 decreases due to the reinforcing effect of the composite reinforced part 9. Also, the composite reinforced part 9 with a volume filling rate of 12% or less is set by the SiC whiskers. When forming a piston, since the strength of the composite reinforcing fiber preform is weak, manufacturing problems arise in that the composite reinforcing portion 9 may crack during the TRF construction of the piston.

Furthermore, if the upper ffl value of the volumetric filling rate V exceeds this value, cracks 7 (particularly in the first region mentioned above) will occur.
The value was set at a value that tends to increase the occurrence of In addition, when the composite reinforcement part 9 is treated with hard alumite 1'1, the occurrence of a series of cracks 7 further increases in accordance with the -1- analogy of the volume filling factor (■) (it turns out that there is a direction of 1). Furthermore, this tendency to increase power is more pronounced when alumina fibers are used than when 5iC whiskers are used.This is because the thermal conductivity of alumina fibers is lower than that of SiC whiskers. Volume filling rate of alumina fiber■.

This is because the thermal conductivity of the composite reinforced portion 9 decreases as the value increases. As a result, the heat generated within the combustion chamber 4 is cut off, and the temperature of the mouth edge 12 rises more than the temperature of the outer circumference, so that the temperature gradient near the mouth edge 12 becomes steeper. Therefore, a larger thermal stress is generated in the mouth edge portion 12.

Further, when the composite reinforced portion 9 is formed of metal fibers such as stainless steel fibers, it is necessary to perform hard alumite treatment after masking the composite reinforced portion 9. This is because if the hard alumite treatment is performed directly on the composite reinforcement part 9, the metal fibers will melt during the treatment and the melt will be released into the electrolytic solution.
This is because the effect of composite reinforcement is completely lost.

Furthermore, the composite reinforcement part 9 has a pair of mutually opposing regions (the above-mentioned second
It is better to limit it to This means that if the rim 12
When the composite reinforcement part 9 is formed in the $■ area around the entire circumference of the
This is because the effect of suppressing the occurrence of 12 is reduced.

Furthermore, when manufacturing a piston composite reinforced with inorganic fibers, the piston 1 may be cast by a pressure casting method. This is because simply pressurizing the piston 1 has the effect of suppressing the occurrence of the 9L crack 7, so if this is combined with the effects of composite reinforcement and hard alumite treatment, the occurrence of the crack 7 can be further suppressed. This is because it is possible. As a result of experiments, the pressure during the pressure casting was 500 kg/am'' to 2,000 kir/c.
It has been found that values within the range of s' are suitable.

As is clear from the above, cracks 7 that occur in the mouth edge 12 of the combustion chamber 4 of the aluminum alloy piston 1 for a direct injection diesel engine, which has a concave combustion chamber 4 on its top surface 11, can be suppressed. It has been found that it is extremely effective to configure the piston 1 as follows.

a) A pair of mutually opposing regions (
The above second region) is compositely reinforced with inorganic fibers. After the composite reinforcement is performed in this manner, almost the entire remaining area of the top surface 11 excluding the composite reinforcement portion 9 is subjected to hard alumite treatment to provide the hard alumite treatment portion 8, or alternatively,
The entire circumference of the mouth edge 12 on the top surface 11 except for the second area is treated with ``entire hard aluminium'' to form the hard alumite treated part 8. In this case, the generation of cracks 7 can be suppressed very effectively compared to the case where only hard alumite treatment is performed. Note that hard alumite treatment may be applied to the entire area of the top surface 1 or the entire circumference of the mouth edge 12 on the top surface 11, although the above-mentioned suppressing effect is slightly weakened.

1 day h) Stainless steel lz (if metal fibers such as 51 are glued to form a composite reinforced part 7, this composite reinforced part 9 is masked and hard aluminium I treatment is performed 1ζ-).

C) Front beam for composite reinforcement! SiC Uiskar, =-Rumi + j3k Iff, 7), Bisuko 71z
Sui! If +'r ¥1'' is used, the volume of 41 and 1i''V'' should be 12-35%, 7-309< and 15-40% (1) Pressure casting [piston] is cast by the method.

In this case, the 21J effect of a), h) and C) above can be further promoted.

Although the present invention has been described above with reference to its embodiments, various changes and modifications can be made to the above-described embodiments as long as they do not deviate from the principles of the present invention.

For example, in the real jK example described in -1-, the top of piston 1 @1]
Although only the hard alumite treatment is applied to the combustion chamber 4, the inner peripheral surface and the bottom surface of the combustion chamber 4 may be entirely or partially subjected to the hard alumite treatment.

〔Effect of the invention〕

As described above, according to the present invention, the piston OTT
111 (7
) In the direction of f + chi at least piston bin], it does not exist in the 100th surface of the song record, and with the direction of ``↑ro-41 area ku・combined reinforcement with the cylindrical machine Uξ fiber'', there is less. No hard alumite treatment is applied to the 441iii YrJ surface,
1. Sea urchin 7.

For this reason, thermal stress and mechanical [(-1 force j'z
A crack appeared at the mouth of the samurai chamber at the 11th part) 1. The crack appeared at the mouth of the samurai chamber. - I can lie down.

[Brief explanation of drawings]

Fig. 1 is a schematic perspective view of a piston with a portion cut away in an embodiment in which the present invention is applied to an aluminum alloy piston for a first generation diesel engine with direct injection, and Fig. 2 shows a composite reinforced portion formed. Graph showing the total amount of cracks generated per piston, Figure 3 shows a conventional aluminum alloy for direct injection diesel engines with a partially cut-out shape. FIG. 4 is a schematic perspective view of a part of a conventional aluminum alloy piston for a direct injection diesel engine, which is different from FIG. 3. In addition, in the symbols used in the drawings, 4-・----Combustion chamber 8...----Alumite treatment part 9 ・-
-------Composite reinforcement part 11-・----・Blood deposit] 2--111 It is the rim of the mouth.

Claims (1)

[Scope of Claims] 1. In an aluminum alloy piston for an internal combustion engine having a concave combustion chamber on its top surface, at least the mouth edges of the combustion chamber that are located on the top surface in the direction of the piston pin and that are opposite to each other. An aluminum alloy piston for an internal combustion engine, characterized in that a pair of regions are compositely reinforced with inorganic fibers, and at least the top surface is subjected to hard alumite treatment. 2. The aluminum alloy piston for an internal combustion engine according to claim 1, wherein the remaining area of the top surface except for the pair of areas is subjected to hard alumite treatment. 3. The aluminum alloy piston for an internal combustion engine according to claim 1, wherein the remaining area of the top surface excluding the composite reinforced portion is subjected to hard alumite treatment. . 4. The aluminum alloy piston for an internal combustion engine according to claim 1, wherein a pair of mutually opposing regions of the mouth edge portion that exist in a direction perpendicular to the piston pin are not compositely reinforced. . 5. Any one of claims 1, 2, 3, or 4, characterized in that the volume filling rate of the inorganic fibers in the composite reinforced portion is 7% to 40%. The aluminum alloy piston for internal combustion engines according to item 1.