JPS6245964A - Heat insulating piston and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture a heat insulating piston having the superior durability in a simple and easy way by arranging a heat-resisting metal plate onto the outermost surface of the piston top surface and forming a heat insulating layer made of the substance such as ceramics having a low thermal conductivity so as to contact with the back surface of the heat-resisting metal plate. CONSTITUTION:The outermost surface of a piston top surface part is formed from the heat-resisting metal plate 2 having a combustion chamber recessed part 1 formed, and the peripheral edge part 2A is bent nearly perpendicularly to the piston top surface, and the top edge 2B of the bent peripheral edge part 2A is turned back further outside. The peripheral edge part 2A is buried into the basic metal such as aluminium alloy which constitutes the piston basic material part 3. Further, a heat insulating layer 5 made of the composite material integrally composed from the basic metal and the low thermal conductivity substance such as ceramics is interposed between the heat- resisting metal plate 2 and the basic material part 3. Said heat insulating layer 5 is installed in the contact state with the back surface of the heat-resisting metal plate 2 at the position of the combustion chamber recessed part 1 and its peripheral surface so as to correspond to the highest-temperature part of the piston top surface.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a piston for an internal combustion engine such as a diesel engine used in an automobile, particularly a piston having a heat-insulating structure near its top surface, and a method for manufacturing the bis 1-hen. It is.

BACKGROUND OF THE INVENTION In recent years, in diesel engines, in order to raise the temperature of the combustion chamber of the engine to improve fuel efficiency and to prevent incomplete combustion at the initial stage of engine startup, it has been considered to make the top surface of the piston insulated.

Methods for insulating the top of the piston include spraying ceramic on the top of the piston, bonding a ceramic plate to the top of the piston, and making the top of the piston composite with a low thermal conductive material. However, the most effective means for providing essential characteristics to an insulated piston, such as high heat insulation, heat resistance, and thermal shock resistance, is to improve the top surface of the piston. There is a known method in which a cavity (air gap) is formed directly under the cavity and the cavity is used to provide insulation, and the top surface is made of a heat-resistant material in order to cope with the rise in temperature of the top surface due to the insulation. There is.

Specifically, the top surface is formed of a heat-resistant material made of a superalloy such as Inconel, and a cavity for heat insulation is provided between the top heat-resistant material and the piston base material, and the two are bolted together. Adiabatic pistons are known.

Problems to be Solved by the Invention As mentioned above, in the conventional heat-insulating piston in which the heat-insulating cavity is formed directly under the top heat-resistant metal plate, since the bottom surface of the heat-resistant metal plate is hollow, the combustion pressure during piston operation The heat-resistant metal plate is easily deformed by the heat-resistant metal plate, and to prevent this, the thickness of the heat-resistant metal plate must be made considerably thicker. There is a problem that it adversely affects fuel consumption and engine P1 performance, and there is also a problem that leads to high cost. Furthermore, in the conventional cavity insulation type piston mentioned above, the top heat-resistant metal plate is joined to the base material by bolt 1, but with this structure, the bolt seating surface and bolt hole of piston mu are subject to creep deformation. There was a problem in that the bolts became loose due to this, and the joint strength between the top heat-resistant material and the tongue gradually decreased, and therefore sufficient durability could not be obtained.

This invention has been made to solve the above-mentioned problems using bronze, and provides an insulating piston in which the top surface is formed of a heat-resistant metal plate and a heat-insulating layer is interposed between the curved heat-resistant alloy plate and the piston material metal. The structure is designed to sufficiently prevent deformation of the top surface even if the thickness of the heat-resistant metal plate is reduced, thereby simultaneously achieving weight reduction of the piston and improvement of the deformation resistance and durability of the top surface. The basic objective is to provide a thermally insulated piston with a A second object of the present invention is to provide an adiabatic piston having a structure in which the bonding bullet holes of the top heat-resistant metal plate to the base material do not deteriorate, thereby further improving durability. A further object of the invention is to provide a method for manufacturing a piston as described above, which is actually simple and easy.

Means for Solving the Problems This invention provides a heat-resistant metal plate made of a material with higher heat resistance than the piston material metal on the outermost surface of the top surface of the piston, and a heat-resistant metal plate made of a material having higher heat resistance than the piston material metal, and in contact with the back surface of the heat-resistant metal plate. ,
It is characterized in that a heat insulating layer is formed by compositely integrating a substance with a lower thermal conductivity than the piston base metal and the piston base metal.

Further, in the piston of the present invention, the heat-resistant metal plate is fixed to the base metal by embedding the peripheral edge of the heat-resistant metal plate in the piston base metal.

Furthermore, in the method for manufacturing a heat-insulating piston of the present invention, when manufacturing a piston by pressure casting, a heat-resistant metal plate is arranged so as to be in contact with the bottom surface of a casting mold, and the negative side of the heat-resistant metal plate is placed on the negative side of the heat-resistant metal plate. A porous body made of a material with lower thermal conductivity than the piston material metal is placed, and in this state, the piston base metal molten metal is poured into the mold and the base metal molten metal is pressurized. This method is characterized in that the mass is impregnated with molten base metal and the heat-resistant metal plate is cast inside.

Function: In the heat-insulating piston of the present invention, as described above, the heat-insulating layer provided in contact with the back surface of the outermost heat-resistant metal plate on the top surface of the piston is a composite of a low thermal conductivity material such as ceramic and a base metal. Constructed from an integrated composite material. Such a composite material also has a thermal conductivity lower than that of the base metal, so that the top surface of the piston can be effectively insulated by the composite insulation layer. Moreover, the heat insulating layer is not a hollow part as in the conventionally known technology mentioned above, but is made of a composite material with high strength, so the composite heat insulating layer absorbs the combustion pressure that is applied to the top heat-resistant metal plate when the piston is operating. As a result, deformation of the top heat-resistant metal plate can be prevented, and therefore the thickness of the top heat-resistant metal plate can be made much thinner than in the case of a cavity heat-insulating structure. Therefore, in the heat-insulating piston of the present invention, by making the heat-resistant metal plate on the top surface thinner, it is possible to significantly increase the lifting height of the piston compared to a piston having a hollow heat-insulating structure. In addition, if the heat-resistant metal plate on the top surface is fixed to the base material by embedding the end of the heat-resistant metal plate in the material metal, as in the case of the prior art, the creep deformation of the base H will cause the heat-resistant There is little risk of reducing the bonding strength between the metal plate and the base material.
Therefore, the durability as a screw can be further improved.

Furthermore, in the method for manufacturing a heat-insulating piston of the present invention, the piston fR sacrificial metal melt is pressure cast, and the material metal and the porous material with low thermal conductivity are integrated into a composite material. The heat-insulating layer is formed continuously and integrally with the base metal portion, and at the same time, the heat-resistant metal plate constituting the topmost surface is cast into the base metal, thereby fixing the heat-resistant metal plate to the workpiece. In other words, the formation of the composite heat insulating layer directly under the curved surface and the fixation of the top heat-resistant metal plate are performed simultaneously with the casting of the base material, making it possible to easily manufacture a heat insulating piston with excellent properties as described above. can do.

Specific instructions for carrying out the invention FIG. 1 shows an example of the structure of the heat insulating piston of the present invention.

Note that FIG. 1 shows an example of a piston in which four combustion chamber parts 1 are formed on the top surface of the piston.

In FIG. 1, the outermost surface of the top surface of the piston is formed of a heat-resistant metal plate 2 molded with the combustion chamber recess 1, and the peripheral edge 2A of this heat-resistant metal plate 20 is bent approximately at right angles to the top surface of the piston. While being bent, the tip 2B of the bent peripheral edge portion 2A is further folded back toward the outer circumference. The peripheral edge portion 2A of such a heat-resistant metal plate 2 is embedded in a base metal such as an aluminum alloy that constitutes the piston material portion 3. That is, the outermost peripheral edge of the top surface of the piston is formed by a composite part 4 in which a base metal is impregnated with a porous body such as ceramic mH, and the base metal/
The peripheral edge part 2A of the heat-resistant metal plate 2 is sandwiched between the composite part 4 made of a porous body and the 1/- Il material part 3, so that the peripheral edge part 2A is embedded in the base metal.

Further, between the heat-resistant metal plate 2 and the base material portion 3, there is interposed a heat insulating layer 5 made of a composite material in which a material with low thermal conductivity such as ceramic and a material metal are integrated. The mixed material heat insulating layer 5 is formed in contact with the back surface of the heat-resistant metal plate 2 at the four combustion chamber parts 1 and its surroundings so as to correspond to the highest temperature portion of the top surface of the piston.

The heat-resistant metal plate 2 may be made of a material that has better heat resistance than at least the base metal (ΔQ alloy, etc.), that is, a material that has better high-temperature strength than the base metal, and also has high-temperature oxidation resistance. It is also desired that the material has excellent high-temperature corrosion resistance. From this point of view, the material for the heat-resistant metal plate 2 is 5
Stainless steel such as US304 or JIS SU
H-based heat-resistant steels, as well as Fe-based heat-resistant alloys such as Incoloy (Fe-based super superalloys, Ni-based heat-resistant alloys such as Incoloy)
CO-based heat-resistant alloys (G
O-based superalloys), JISSCH-based Im, Ti alloys, etc. can be used. In addition, in the heat-insulating piston of the present invention, it is desirable that the heat-resistant metal plate itself constituting the top surface has some degree of heat-insulating properties, and in that sense, it is desirable to use an alloy with low thermal conductivity as the heat-resistant metal plate. Therefore, alloys such as Fe-based, N1-based, CO-based, etc. are optimal.

The composite material constituting the heat insulating layer 5 may be one in which a base metal such as Aj7 alloy and a substance having a thermal conductivity lower than that of the base metal are integrated. Various materials can be selected as the low thermal conductivity material, but it is desirable that the material has as low a thermal conductivity as possible and is stable at the melting point of the base metal, and in this sense, ceramic is most suitable. Among ceramics, it is particularly desirable to select a ceramic that is stable even at the piston top surface temperature (approximately 700 to 800°C) during operation.
02, TiC, BN, MOSt2, etc. can be used. In addition, various oxides, carbides, nitrides, silicides, or mixtures thereof can be used. Various refractory ceramics can also be used, such as perlite, mica, and mullite. Furthermore, the low thermal conductivity material can be used in various forms before being composited, such as particulate, 111t, foam, and box shapes.

In the structure example shown in FIG. 1, the outermost peripheral edge of the top surface of the piston is a composite part 4, and the peripheral part 2A of the heat-resistant metal plate 2 is embedded in the base metal by this composite part 4. However, the outermost peripheral edge of the top surface of the piston does not necessarily have to be a composite part.

In any case, by embedding the peripheral edge 2△ of the heat-resistant metal plate 2 into the metal material, the heat-resistant metal plate 2 can be firmly joined to the base metal portion 3 without using separate fixing means such as bolts. Can be fixed.

When the peripheral edge 2A of the heat-resistant metal plate 2 is embedded in the base metal in this way, various shapes such as those shown in FIGS. can do.

Further, the shape of the top surface of the piston is not limited to the shape shown in FIG. 1, but can be applied to various shapes as shown in FIGS. 3(A) to 3(D).

Furthermore, the mixed material heat insulating layer 5 interposed between the top heat-resistant metal plate 2 and the base material portion 3 corresponds to at least the hottest part of the top surface of the piston, and the heat-resistant metal plate 2 in that part In addition to the arrangement shown in FIG. 1, the arrangement shown in FIGS. 4(A) to (D) can be applied.

As a method for manufacturing the heat insulating piston of the present invention as described above, a pressure casting method such as high pressure casting can be applied.

A specific example of the manufacturing method using high-pressure casting will be described for the case of manufacturing the heat-insulating piston shown in FIG. 1. First, as shown in FIG. A porous body 51 of a low thermal conductivity material for forming the composite heat insulating layer 5 and an annular porous body 41 for forming the composite portion 4 at the peripheral edge of the top surface of the piston are combined.

Then, as shown in FIG. 6, these are arranged so that the top surface side of the heat-resistant metal plate 2 is in contact with the bottom surface of the mold 7, and the piston base metal molten metal 8 such as aluminum alloy molten water is poured, preferably at a temperature of 300 kg. (A pressure of approximately 1/c♂ or more is applied to the molten base metal 8, and the pressure is maintained until the molten base metal 8 solidifies. In Fig. 6, 9 is a pressurizing punch; 1
0 is a knockout bin for taking out castings.

When high-pressure casting is performed in this way, the base metal molten metal 8 is impregnated into the porous body 51 of the low thermal conductivity material and enters the voids thereof, and the low thermal conductivity material and the material metal are composited into one, and the part is composited. The material becomes the heat insulation layer 5.

Further, a portion of the annular porous body 41 is also impregnated with the material metal,
This portion becomes a composite portion 4 that constitutes the peripheral edge of the top surface of the piston. The heat-resistant metal plate 2 is cast with its peripheral edge embedded in the base metal.

In this way, the composite heat insulating layer 5 is formed so as to be in contact with the back surface of the single-layer plate 2 of the heat-resistant stand 12 forming the topmost surface, and the peripheral edge of the heat-resistant metal plate 2 is embedded in the raw metal. An adiabatic piston as shown in FIG. 1 can be obtained.

In addition, as a low thermal conductivity material constituting the composite material insulation layer 5,
If the form of the particulate low thermal conductivity material before being composited with the base metal is in a form that is difficult to maintain by itself, such as particles, as shown in Example 1 described later, the shape of the particulate low thermal conductivity material is In order to maintain this, it may be covered with a porous body capable of maintaining its shape, such as a ceramic molded body, and placed in a mold in this state and pressure casting may be performed. In this case, not only the particulate low thermal conductivity substance part is integrated with the base metal to form a composite heat insulating layer, but also the part of the porous body such as the ceramic 1llft molded body covering it is also integrated with the base metal. It is combined with material metal to become a composite material. Therefore, in that case, two composite material layers will be formed. In this case, by using a low thermal conductivity material such as ceramic as described above as another porous body covering the particulate low thermal conductivity material, that layer can also be referred to as a composite heat insulating layer, and therefore, for example, As shown in FIG. 7, two composite heat insulation layers 5A and 511 are formed.

Example An example of manufacturing a heat insulating piston having the structure as shown in FIG. 7 is shown below. An alumina short fiber molded body (fiber diameter 3 JJm, fiber length 3 mm, molded body bulk density 0.17 (+/cc)) was prepared. A molded body 52 (ZrO2 volume fraction 50%) made of zirconia powder (particle size 1) and paraffin and having the shape and dimensions as shown in FIG. 8(B) was prepared. Furthermore, the heat-resistant metal plate 2 is 5U with a plate thickness of 2 mm.
This is shown in Figure 8 (C) using a stainless steel plate made of S304 steel.
Not shown in Figure 8 (D).
) as shown in the alumina short fiber molded body (bulk density 0.1
7(]/cc) was prepared. After these are combined as shown in FIG. 9, the combined body 21 is heated to 400° C. in the atmosphere to completely burn off the paraffin in the compact 52, and the compact 52 is converted into 7r02 particles. The porous portion 51 was made of only the above-mentioned.

Next, as shown in FIG. 10, the assembled body 21 was placed in a high-pressure casting mold 7 so that the top side of the heat-resistant metal plate 2 was in contact with the bottom surface of the mold, and was cast in a JIS AC8 molding machine with a hot water temperature of 720°C.
A aluminum alloy melt 1 (Aβ-12%3i-1,2
%CI -1,0%M! +-2%Ni-〇, 3%Fe)
8 was poured and high-pressure casting was performed by applying a pressure of 500 k (1/ant). This pressure was maintained until the Aβ alloy molten lagoon 8 solidified. As a result, the molten A1 alloy was cast into the alumina short fiber compact 11. and Zr02 particles are impregnated into the porous portion 51 to form a first composite!4 heat insulation layer 5A made of ZrO2 and He1 alloy and a second composite heat insulation layer made of alumina!1H and Hebeta alloy. The layer 5B could be formed, and the part of the annular porous body 41 could be impregnated with the A1 alloy to form the composite part 4, and the heat-resistant metal plate 2 could be embedded in the base material A1 alloy. The β-bis casting material thus obtained was subjected to T7 treatment (solution treatment 490
After performing aging treatment at 220° C. for 4 hours and 8 hours at 220° C., the piston ring grooves 20 and the like were machined, and finally an adiabatic piston as shown in FIG. 7 was obtained.

The adiabatic piston shown in Fig. 7 obtained as above-L is
When installed in a diesel engine and tested for combustion characteristics, it was found that the time and amount of incomplete combustion gas (smoke) was generated compared to conventional aluminum alloy pistons from startup to high load operation. It has been found that the piston is extremely excellent as a piston for diesel engines.

On the other hand, for comparison, a hollow heat-insulating piston having a heat-insulating cavity 12 directly below the top heat-resistant metal plate 2 as shown in FIG. 11 was manufactured in the following manner.

That is, an alumina short fiber molded body (bulk density 0.17 (1/cc) 13) having the shape and dimensions as shown in FIG. 12(A) and an epoxy resin molded body having the shape and dimensions as shown in FIG. 12(B). 14 and 5US30 as shown in Figure 12(C).
A heat-resistant metal plate 2 consisting of 4 and an alumina short plate 2 having the shape and dimensions shown in FIG. 12(D)! iH molded body (0.17o/
cc) 15 were prepared, and these were combined according to the case shown in FIG. 9, placed in the high-pressure casting mold 7, and a JISAC8A aluminum alloy was pressure cast under the same conditions as above, and as shown in FIG. 13. A screw material as shown was obtained. In this state, the portions of the short alumina fiber molded bodies 13.15 are each impregnated with aluminum alloy to form a composite part 16.4, while the epoxy resin molded body 14 still substantially maintains its shape.

Next, as shown by the chain line in FIG. 13, a degassing passage 17 with an inner diameter of 3 lil communicating from the outside of the casting to the epoxy resin molded body 14 was formed, and then T7 treatment was performed under the same conditions as above. Through this T7 treatment, the epoxy resin molded body 14 was burnt and removed, and that portion became the cavity 12. After that, tighten the gas vent passage 17 with stainless steel screws 1.
8 and further machining the piston ring grooves 20, etc., to finally obtain a hollow heat-insulated piston as shown in FIG. 11.

The cavity insulation type piston of the comparative example thus obtained and the above-mentioned composite material insulation type piston according to the example of the present invention were each assembled into a diesel engine and the engine was operated under the same conditions. As a result, both showed extremely good characteristics at idling, but at 440 rpm.

When the condition of the piston was examined after conducting a 50-hour high-load durability test, it was found that the stainless steel plate, which is the heat-resistant metal plate 2, was deformed around the recessed part of the combustion chamber in the hollow insulation type piston. In the composite heat insulating piston according to the example of the present invention, such deformation of the heat-resistant metal plate was not observed at all.

Both the above-described hollow insulated piston and the composite insulated bison according to the present invention use a stainless steel plate with a thickness of 2n+n+ as the heat-resistant metal plate 2, but in the case of the hollow insulated piston, deformation of the stainless steel plate due to combustion pressure is used. It was found that in order to stop the piston, a plate thickness of 4 mm was required, which would increase the piston weight by about 20%. From this, it is clear that the composite heat insulating piston of the present invention can be lighter in weight compared to a cavity heat insulating piston.

Regarding heat insulation properties, it was confirmed that the ceramic heat insulation type piston according to the present invention also has heat insulation properties equivalent to that of the cavity heat insulation type piston.

In addition, as the low thermal conductivity material constituting the composite heat insulating layer, instead of the aforementioned 7"02 particles, an aggregate of disc-shaped foil mica (volume ratio 30%) with a diameter of 10 tones and a thickness of 2 tones is used. An adiabatic piston was made using Z
Instead of r 02 particles, diameter 0.5 mm, volume fraction 30%
When using a foamed pearlite aggregate with a diameter of 3. +
Similar characteristics were obtained when a molded body of mullite fibers (volume ratio: 40%) with a thickness of 1 ml and 1 ml was used.

Effects of the Invention As is clear from the above explanation, the piston of the present invention has the same heat insulation properties as the conventionally known cavity insulation type piston, and the deformation resistance of the top surface is much higher. In addition to exhibiting durability, the thickness of the topmost heat-resistant metal plate can be reduced to reduce the weight of the piston, thereby improving engine performance, fuel efficiency, etc.

In addition, especially in embodiments in which the peripheral edge of the top heat-resistant metal plate is embedded in the piston base material, the bonding strength between the heat-resistant metal plate and the material is effectively maintained, further improving the piston durability. be able to.

Furthermore, according to the manufacturing method of the present invention, the formation of the composite heat insulating layer directly under the top surface and the fixing of the top heat-resistant metal plate by the casting are performed simultaneously with the casting of the base material, which provides the excellent performance as described above. A heat insulating piston having such characteristics can be simply and easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of the heat insulating piston of the present invention, and FIGS. 2 (A) to (1) are schematic diagrams showing other examples of the end shape of the heat-resistant metal plate in the heat insulating piston of the present invention, respectively. , FIGS. 3(A) to 3(D) are schematic diagrams showing examples of the top shape of the adiabatic piston of the present invention, and FIGS. 4(A) to (r)) are schematic illustrations of the adiabatic piston of the present invention It is a schematic diagram showing an example of arrangement of ceramic heat insulating layers. Figures 5 and 6 are diagrams for explaining the manufacturing method of the heat-insulating piston shown in Figure 1. Figure 5 is a longitudinal cross-sectional view showing the assembled state of each member to be cast, and Figure 6 is the base material. FIG. 3 is a longitudinal cross-sectional view showing the situation during metal pouring. FIG. 7 is a longitudinal sectional view showing another example of the heat insulating piston of the present invention. Figure 8 (A) ~
(D) is a cross-sectional view of each member used in manufacturing the piston shown in Fig. 7, and Fig. 9 is a longitudinal cross-section showing the assembled state of each member shown in Figs. 8 (A) to (r)). 10 is a schematic longitudinal cross-sectional view showing a state in which the member shown in FIG. 8 is placed in a mold and molten base metal is poured into the mold. FIG. 11 is a longitudinal cross-sectional view showing an example of a hollow heat-insulated piston as a comparative example, and FIGS. Figure 13 is Figure 12 (A)
It is a longitudinal cross-sectional view which shows the state immediately after casting of the bison material casting which assembled and high-pressure-casted each member shown in - (D). 2...Heat-resistant metal plate, 3...Base material portion, 5...
Composite heat insulation layer, 7...Mold, 8...Metal hot water. Applicant Toyota Motor Corporation Ne1 Agent Patent Attorney Yutaka 1) Hisashi Take (and 1 other person) Dimensions of Figure 1 Figure 5 Figure 7 Figure 8 111 -74mm -1 1+11

Claims (4)

[Claims] (1) A heat-resistant metal plate made of a material with higher heat resistance than the piston base metal is placed on the outermost surface of the top surface of the piston, and a heat-resistant metal plate made of a material with higher heat resistance than the piston base metal is placed so as to be in contact with the back side of the heat-resistant metal plate. A heat insulating piston characterized in that a heat insulating layer is formed by a composite and integrated material of a low-density material and a metal material for the piston. (2) Claim 1, wherein the substance is a ceramic.
Insulated piston as described in section. (3) The heat-insulating piston according to claim 1, wherein the heat-resistant metal plate is fixed by embedding the circumferential end of the heat-insulating metal plate in the piston base metal. (4) When manufacturing a piston by pressure casting, a heat-resistant metal plate is placed so as to be in contact with the bottom of the casting mold, and a metal plate with a thermal conductivity higher than that of the piston base metal is placed on the top surface of the heat-resistant metal plate. A porous body made of a low-density substance is placed, and in that state, the piston base metal molten metal is poured into the mold and the base metal molten metal is pressurized, thereby impregnating the porous body with the base metal molten metal. A method for producing a heat insulating piston, comprising casting the heat-resistant metal plate.