JPS61126358A - Built up piston for engine - Google Patents

Abstract

PURPOSE:To both enhance mass productivity of a piston and reduce its size and weight, by combining a small thickness member of high strength metal alloy with a piston main unit part and a piston head part and connecting these parts by shrinkage fit due to a high temperature. CONSTITUTION:A small thickness member 3, 4 of high strength metal alloy is combined by junction means of cast wrapping or the like with a connection portion between a piston main unit part 1 consisting of light alloy material and a piston head part 2 consisting of ceramic material, respectively. The small thickness member 3, being made of material in an equal system to the small thickness member 4 and formed in a small thickness cylindrical shape with a flange, is integrally connected by cast wrapping with the piston main unit 1. A connection fixed part 6 is finished by processing work with a necessary fitting margin. And the piston main unit part 1, being heated to a high temperature just below the normally applied temperature of a light alloy material, forcedly inserts by temperature difference fit the cooled piston head part 2 of ceramic material to be fitted. In this way, a piston, enhancing its mass productivity, can be formed in small size and in light weight.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a prefabricated piston for an engine.
The piston body made of a light alloy material and the piston head made of a ceramic material are integrally joined or combined with high-strength metal alloy thin-walled members made of the same material, respectively, and the piston body and the piston head are normally connected. An engine that is lightweight, has excellent durability, reliability, and impact resistance, and also has improved natural frequency characteristics by being bonded and fixed in an elastically deformed state with preload applied by baking at a higher temperature. It depends on the prefabricated piston.

[Conventional technology]

It is already well known that engine performance can be improved by disposing a ceramic material in the piston head of an engine piston to improve heat resistance.

It is known that this effect is particularly remarkable in pistons for direct injection diesel engines.

Furthermore, attempts have been made to form the entire piston from a metal material and form a ceramic sprayed layer on the top surface of the piston, which requires heat resistance, but this method has the problem of poor mass productivity.

In addition, in the process of conventional development of high-performance pistons, there is no need to consider space constraints at the laboratory stage, so by creating a configuration that takes up a large space, it is possible to design freely and increase durability. Although there is no problem from a reliability standpoint, the technology to create a piston that is mass-producible, compact, and inexpensive has not yet been perfected.

Now, regarding engine pistons, in the old days,
A method developed by Cummins Inc. in which a piston head made of a ceramic material is simply fixed with bolts to the center of a piston body made of an iron-based alloy material has been attempted; It has not been put into practical use because measures against the coefficient of thermal expansion are insufficient.

On the other hand, recent ceramic materials are said to have excellent strength and are comparable to iron-based alloys, and high-performance pistons are manufactured by casting light alloy materials such as A1 alloy that form the piston body into ceramic materials that form the piston head. However, the excessive thermal stress generated between the A1 alloy and the ceramic material during heat shrinkage due to cooling after casting cannot be ignored, and in addition, the resistance of the ceramic material cannot be ignored. Cracks may occur due to poor impact resistance, or due to the small amount of elastic deformation of ceramic materials, the length may be due to insufficient contact elasticity due to the large difference in coefficient of thermal expansion between light alloy materials and ceramic materials. Currently, it has not been put into practical use due to problems such as insufficient durability and reliability over time.

Another promising method is to combine a piston head made of ceramic material with a piston body made of iron-based alloy casting by using ceramic materials such as ZrO2, which has a thermal expansion coefficient similar to that of iron-based alloys. However, considering the original purpose of the piston, which is to reduce the weight of the piston, this is not a disadvantage.

As mentioned above, the original purpose of the piston itself is to be lightweight, so if A1 alloy is desirable for the piston body, there is a large difference in coefficient of thermal expansion from the ceramic material of the piston head ( Approximately 18X1
Therefore, it is necessary to specifically construct an assembled piston for an engine in which a piston body made of a light alloy material and a piston head made of a ceramic material are combined and fixed as separate parts. was difficult.

By the way, the inventor has already proposed an "assembly-type piston for engines" based on the idea of configuring the piston body and the piston head as separate members, as described above, and in particular, the inventor has proposed a piston made of a light alloy material. We have already proposed a screw structure as a means of locking the piston head made of ceramic material to the main body (
U.S.P.

No. 4343229).

The present invention utilizes the above-mentioned previously proposed inventions and makes improvements to further improve its practicality.

[Problem that the invention seeks to solve]

In view of the current state of the prior art as described above, the problem to be solved by the present invention is to form the piston body made of a light alloy material and the piston head part made of a ceramic material as separate members, and to integrate them into one piece. In conventional assembled pistons for engines that are connected and fixed to the piston, there is a difference in the coefficient of thermal expansion between the two, and the impact resistance of the ceramic material used as the piston head.

Although it has sufficient durability and reliability in the laboratory due to its low plastic deformability, it has not yet been technically perfected as a practical engine piston in terms of mass production, compactness, and low cost. This is something that has not been done.

Therefore, the technical problem of the present invention is that instead of employing the conventional direct coupling and fixing means such as shrink fitting between different materials, the piston body is made of a thin-walled high-strength metal alloy member. mass production of assembled pistons for engines by using a piston head section in which a high-strength metal alloy thin-walled member is combined with a high-strength metal alloy thin-walled member as a means for connecting and fixing the high-strength metal alloy thin-walled members by shrink-fitting at higher temperatures than usual. In addition to increasing its practicality by ensuring flexibility, compactness, and low cost, it is also lightweight, has excellent impact resistance, long-term durability reliability, and impact resistance, and also improves natural frequency characteristics. .

[Means for solving problems]

In view of these problems in the conventional technology, the present invention provides means for solving the problems in the conventional technology by combining a piston body made of a light alloy material and a piston head part made of a ceramic material. A fixed assembly type piston for an engine, wherein the piston main body made of the light alloy material has a high strength material having a coefficient of thermal expansion intermediate between that of the light alloy material and the ceramic material at the joint/fixation part with the piston head part. The metal alloy thin-walled member is joined by a joining means such as a casting, and on the other hand, the metal alloy joined to the piston body by a joining means such as a shrinkage fit is attached to the joining/fixing part of the piston head made of ceramic ivy material. High-strength metal alloy thin-walled members of the same type of material are combined, and a light alloy material is used for the piston body to which the above-mentioned high-strength metal alloy thin-walled members are combined and the piston head to which the above-mentioned high-strength metal alloy thin-walled members are combined. By heating the piston body to a high temperature just below the heating deformation temperature and cooling the piston head, the piston head can be press-fitted by reducing the fitting allowance for temperature difference fitting. From an assembly type piston for an engine, which is characterized by being press-fitted into the piston body and fixed and connected.
! It has become.

[Effect]

Hereinafter, the effects of the present invention will be explained.

In the present invention, a piston body made of a light alloy material and a piston head made of a ceramic material are combined and
A fixed assembly type piston for an engine, wherein the piston main body made of the light alloy material has a high strength material having a coefficient of thermal expansion intermediate between that of the light alloy material and the ceramic material at the joint/fixation part with the piston head part. The metal alloy thin-walled member is connected by a joining means such as a casting, and on the other hand, the metal alloy is connected to the piston body by a joining means such as a shrinkage fit to the joining/fixing part of the piston head made of a ceramic material. 1. Join high-strength metal alloy thin-walled members made of similar materials. The piston main body to which the high-strength metal alloy thin-walled member is combined is coupled to the high-strength metal alloy thin-walled member because:
When the piston body and the piston head are connected and fixed, the high-strength metal alloy thin-walled member of the piston body and the high-strength metal alloy thin-walled member of the piston head are combined and fixed as an integral piston. This is to avoid direct bonding and fixation between the light alloy material that makes up the piston body and the ceramic material that makes up the piston head.

In addition, in the present invention, the high-strength metal alloy thin-walled member connected to the piston body and the high-strength metal alloy thin-walled member connected to the piston head are made of high-strength metal alloys of similar materials, and the thin-walled member structure is When press-fitting and fitting the piston body and piston head by temperature difference fitting, a temperature difference is generated between the piston body and the piston head due to changes in ambient temperature (<, therefore, This is because the preloaded state at the time of fitting is maintained.

In addition, in the present invention, the metal alloy used as the high-strength metal alloy thin-walled member only needs to be high-strength and have a coefficient of thermal expansion intermediate between light alloy materials and ceramic materials, such as high-strength iron-based alloys, high-strength Titanium alloy or the like can be suitably used.

In addition, the high-strength metal alloy thin member may be a thin member in terms of shape, as long as it is a shape that can be firmly joined or coupled to the piston body and the piston head.

Further, in the present invention, the piston body made of a light alloy material is heated to a deformation temperature for the piston body to which a high-strength metal alloy thin-walled member is combined and the piston head to which the above-mentioned high-strength metal alloy thin-walled member is combined. The piston head is press-fitted and fitted into the piston body by using a fitting allowance for temperature difference fitting, which allows the piston head to be press-fitted and fitted by cooling the piston head and making it directly below the high temperature. 6, which is supposed to be fixed and connected together.
By press-fitting and fitting the piston body and the piston head through temperature differential fitting, the high-strength metal alloy thin-walled member of the piston body and the high-strength metal alloy thin-walled member of the piston head, which have the same coefficient of thermal expansion, form the piston body. This is to connect and fix the piston head part and the piston head part in an elastically deformed state with a preload applied by shrink fitting at a higher temperature than usual.

Furthermore, in the present invention, the high-strength metal alloy thin member to be joined to the piston body made of a light alloy material and the piston head made of a ceramic material is made of a material having a coefficient of thermal expansion intermediate between that of the light alloy material and the ceramic material. This is to alleviate the difference in thermal expansion coefficients between the piston body and the piston head, and to improve the state of connection and fixation between the two in the assembled piston.

Further, in the present invention, after the piston main body and the piston head are joined and fixed, welding is performed using high-density energy such as a laser beam on the joint and fixed parts of the high-strength metal alloy thin-walled members. This is effective because it strengthens the connection and fixation between the two and improves the natural frequency characteristics and properties of the piston.

Further, in the present invention, the material of the ceramic material constituting the piston head portion is not particularly limited, and may include Si, N4, well-known so-called fine ceramics. SiC, ZrO2゜AI 20. Various ceramic materials such as can be suitably applied.

〔Example〕

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

(First Embodiment) FIG. 1 is a diagram showing a first embodiment of an assembly type piston for an engine according to the present invention.

In Fig. 1, 1 is the piston body, 2 is the piston head, 2a is the cavity at the top of the piston, and 3 is the connection between the piston body 1 and the piston head 2.
A high-strength metal alloy thin-walled member having an intermediate coefficient of thermal expansion between a light alloy material and a ceramic material is connected to the fixing part 6 by casting, 4 is a connecting/fixing part 6 with the piston body part 1 in the piston head part 2, A high-strength metal alloy thin-walled member coupled by shrink fit; 4a is a threaded portion for fitting the high-strength metal alloy thin-walled member 4 of the piston head portion 2;
4b is a piston head portion 2 and a high-strength metal alloy thin-walled member 4
5 is an integrated casting part, 6 is a joining/fixing part between the piston body part 1 and the piston head part 2 which are press-fitted and fitted by temperature difference fitting, and 7a is a partial welding part. , 8
The pressure receiving plane portion +9a is the upper opening of the piston body portion 1.

In this embodiment, a thin-walled high-strength metal alloy member 3 having a thermal expansion coefficient intermediate between that of a light alloy material and a ceramic material is attached to the connecting/fixing part 6 of the piston body part l to the piston head part 2. are connected by.

In addition, a high-strength metal alloy thin-walled member 4 made of the same type of metal alloy as the metal alloy bonded to the piston body 1 is connected to the piston head 2 in a screw structure to a connection/fixation portion 6 with the piston body 1. has been done.

The present invention improves the possibility of practical application of the conventional assembled piston for engines, and the fourth embodiment has a screw fastening structure between the piston head portion 2 and the high-strength metal alloy thin member 4 to further strengthen the fastening. It was made into something.

Further, there is a temperature difference between the piston body 1 to which the high-strength metal alloy thin-walled member 3 is connected and the piston head 2 to which the high-strength metal alloy thin-walled member 4 is connected at the cylindrical portion (joint/fixed portion 6) having a diameter φD. They are press-fitted and connected by fitting (for example, by shrink fitting).

Next, a method for manufacturing the assembly type piston for an engine shown in FIG. 1 will be explained based on FIG. 2.

First, as shown in FIG. 2(a), St zNa, SiC, Zr
A piston head portion 2 made of a ceramic material such as OzOi or AlzOi is molded and fired, and the pressure-receiving flat portion 8 and threaded portion 4b are slightly finished so as to fall within the standard dimension range.

Note that in this step, the finishing process may be omitted by interposing a shim portion.

Next, as shown in FIG. 2(b), the piston head portion 2
A high-strength metal alloy thin-walled member 4 to be screwed together is manufactured.

In this case, it is usually desirable to use spring steel as the high-strength metal alloy thin member 4, but even ordinary steel can be used as it is within the range where sufficient elastic deformation can be utilized.

Next, this high-strength metal alloy thin member 4 is processed into a shape that matches the thread shape of the piston head portion 2.

What should be noted in this process is that it is not a normal thread shape, but a thread shape that has a fit allowance for shrink fit.

Further, the thickness of the high-strength metal alloy thin member 4 is naturally determined by the balance between the shrink fit temperature and the stress required for tensile fastening.

On the other hand, as shown in FIG. 2(C), the high-strength metal alloy thin member 3 has a thin cylindrical shape with a flange made of the same material as the high-strength metal alloy thin member 4, and is integrated into the piston body 1 by casting. are connected to each other.

Further, the coupling/fixing portion 6 is finished with a required fitting allowance.

In particular, the press-fitting/fitting allowance for temperature differential fitting of the coupling/fixing part 6 is also a key point of the present invention, and must be properly managed.

In this way, the piston head section 2 made of a ceramic material cooled with dry ice or the like is press-fitted and fitted into the piston body section 1 heated to a high temperature just below the heating temperature of the light alloy material by temperature differential fitting. .

At this time, even if the piston head part 2 is cooled to a low temperature by a cooling means such as dry ice, if the piston body part 1 is an A1 alloy, the heating temperature is set to a high temperature that is substantially just below the heating deformation temperature. Even if the stress is applied, the high-strength metal alloy thin members 3 and 4 can sufficiently withstand the stress.

Moreover, within the operating temperature range of the piston, residual stress is not released, and sufficient fastening force can be ensured.

Further, with the open piston main body structure shown in FIG. 1, the oil can be sufficiently cooled to a constant temperature by the lubricating oil 11 that scatters.

Although a partial welded part is shown in 7a, this is for reinforcement and is not necessarily necessary.The cylindrical part that will become the joining/fixing part 6 is divided into equal parts by laser beam welding or the like. It is only necessary to perform partial welding at several points, and this reinforcement by welding prevents resonance of the piston due to its natural frequency characteristics and contributes to its effectiveness.

(Second Embodiment) FIG. 3 is a diagram showing a second embodiment of an assembly type piston for an engine according to the present invention.

In this second embodiment, the same or corresponding parts as those in the first embodiment shown in FIG. 1 are given the same reference numerals as in FIG. 1, and the explanation thereof will be omitted.

When compared with the first embodiment, the second embodiment has a straight thread in the portion of the piston head 2 that is connected and fixed to the piston body 1, as shown in FIG. It has a cylindrical surface.

The thin cylindrical body 4 is made of, for example, an iron-based alloy, and subjected to a high-temperature heating shrink fit, which is higher than that of a normal shrink fit.

In this way, by shrink-fitting by heating at a higher temperature than usual, excessive thermal stress is generated in the cooling process after shrink-fitting, and the residual compressive stress of the preload is absorbed by the ceramic material in an elastically stretched state due to elastic deformation. This applies to the piston head portion 2.

Moreover, since fine ceramics such as 5iiN4 are materials with excellent compressive strength, they can sufficiently withstand the above-mentioned residual compressive stress.

In addition, compared to the residual compressive stress during casting of the ceramic material mentioned above, due to the lower heating temperature,
Needless to say, the thinner the wall, the more advantageous it is.

After shrink-fitting and cooling to room temperature as described above, finishing is performed again, and in the next step, the piston head portion 2 to which the high-strength metal alloy thin-walled member 4 is joined is cooled with a coolant such as dry ice. On the other hand, the piston body 1 to which the high-strength metal alloy thin member 3 is bonded is heated to just below the heating deformation temperature of the A1 alloy, and the piston head 2 is press-fitted into the piston body 1 by temperature differential fitting ( For example, they are joined by sintering.

In addition, in the present invention, the surface roughness for shrinkage in the fitting part 4c and the joining/fixing part 6 between the piston body part l and the piston head part 2 is determined by the high-strength metal alloy thin-walled member 3.
This does not pose a problem because 4 and 4 are of the same type of material, and because the shrink fit is a high temperature shrink fit compared to a normal shrink fit.

In addition, as shown in FIG. 1 in the first embodiment, the skirt side of the piston main body 1 has an opening 9a, whereas in the second embodiment, the bottom is closed as shown in FIG. Since the shape is attached, in order to strengthen the partial welded part 7b by laser beam welding etc., it is necessary to drill the drill hole 1.
It is necessary to drill holes in several locations and perform partial welding such as laser beam welding.

Further, the piston main body l has an opening structure as in the first embodiment so that the high-strength metal alloy thin-walled members 3 and 4 of the coupling/fixing part 6 of the first embodiment can be cooled by the cooling oil 11. Needless to say, depending on the conditions, it is possible to make the opening of the piston body 1 of the first embodiment into a closed type reinforcement structure as in the second embodiment. Nor.

〔Effect of the invention〕

As is clear from the above, according to the engine assembly type piston according to the present invention, instead of employing a direct connection and fixing means such as the conventional heat-fitting method between different materials, the high-strength metal alloy thin wall By using a piston body part with joined parts and a piston head part joined with a high-strength metal alloy thin-walled member, the high-strength metal alloy thin-walled members are used as a means for joining and fixing the shrinkage at higher temperatures than usual. In addition to ensuring mass production, compactness, and low cost of assembly-type engine pistons, they have increased practicality, are lightweight, have excellent impact resistance, long-term durability, reliability, and impact resistance, and have a low natural frequency. There is an advantage that the characteristics can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of an assembled piston for an engine according to the present invention. FIG. 2 is an explanatory diagram showing the process of manufacturing the assembly type piston according to the first embodiment of the present invention. FIG. 3 is a longitudinal cross-sectional view showing a second embodiment of an assembled piston for an engine according to the present invention. 1------ Piston main body. 2・----Piston head part. 2a------Cavity part. 3.4 - High strength metal alloy thin wall member. 4 a -------- Threaded portion. 4b・----Threaded fitting part. 4cm --- One cylindrical fitting part. 5-------・Casting part. 6-----One connection/fixation/part. 7 a, 7 b---Partially welded part. 8-・-・-Pressure receiving flat part. 9a -- Piston opening. 9b---Piston center bottom plate part. 10------Drill hole. 11-...-Cooling oil. D-----Fitting diameter. Applicant: Toyota Motor Corporation Figure 1 Figure 2 (b) Figure 3

Claims (1)

[Scope of Claims] 1. An assembled piston for an engine comprising a piston body made of a light alloy material and a piston head made of a ceramic material, the piston body made of the light alloy material. A high-strength metal alloy thin-walled member having a coefficient of thermal expansion intermediate between that of a light alloy material and a ceramic material is connected to the joining/fixing part with the piston head part by a joining means such as a casting, and the other part is made of a ceramic material. A high-strength metal alloy thin-walled member made of the same material as the metal alloy bonded to the piston body is connected to the connecting/fixing portion of the piston head by a connecting means such as shrinkage fit, and the high-strength metal alloy thin-walled member is connected to the piston head at the connecting/fixing portion. By heating the piston body made of a light alloy material to a high temperature just below the heating deformation temperature and cooling the piston head, , an engine characterized in that the piston head is press-fitted and fitted into the piston body to be fixed and connected by providing a fitting allowance for temperature difference fitting that allows the piston head to be press-fitted and fitted. Assembly type piston.