JP2001041099A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston for internal combustion engine which can increase a strength, heat radiation property and toughness and make thin and light, while ensuring the anti-wear property and anti-bite property equal to the past. SOLUTION: The piston 1 for an internal combustion engine is composed of a low Si content aluminium alloy with 10% or less of Si content and a surface treatment for increasing the anti-wear property and anti-bite property is applied thereon. According to this, as the low Si content aluminum alloy with higher fatigue strength, tensile strength (especially high temperature strength) and toughness than a high S content material is selected as the material of the piston 1 in place of the high Si content material of usual AC8, AC9 system containing 10∼20% of Si, the piston 1 can be thin designingly. In regarding to the anti-wear property and anti-bite property, the problem can be solved by giving a proper surface treatment responding to the function to the position requesting them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a piston for an internal combustion engine.

[0002]

2. Description of the Related Art A piston for an internal combustion engine reciprocates in a cylinder.
Aluminum alloys containing -20% Si have been used. This kind of high Si content material contains primary S
The i crystal has the effect of improving the wear resistance and galling resistance of the sliding surface of the piston with the cylinder.

[0003] Further, since the material having a high Si content has a small coefficient of linear expansion, it is convenient for securing a clearance between the piston and the cylinder.

[0004]

However, the high Si content material has poor toughness, and the elongation of ordinary wrought material at room temperature is 10%.
On the other hand, the high Si-containing material shows a very small value of about 3%. For this reason, the fatigue strength is apt to decrease, and it is difficult in design to reduce the weight by reducing the thickness of the piston, and consideration must be given to the occurrence of cracks, and the tensile strength generally also decreases.

Further, since the addition of Si deteriorates the thermal conductivity, the use of a material having a high Si content in a piston exposed to a high temperature is disadvantageous for the problem of heat radiation from the piston to the cylinder.

The present invention has been made in view of the above problems, and has as its object to improve the strength, heat dissipation and toughness while maintaining the same abrasion resistance and galling resistance as in the past, and to reduce the thickness and weight. It is an object of the present invention to provide a piston for an internal combustion engine that can be made more compact.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a piston for an internal combustion engine is made of Si.
It is characterized by being made of a low Si content aluminum alloy having a content of less than 10% and subjected to a surface treatment for enhancing abrasion resistance and galling resistance.

According to a second aspect of the present invention, in the first aspect, the surface treatment is performed on an outer peripheral surface of an internal combustion engine piston and an inner peripheral surface of a piston pin hole.

According to a third aspect of the present invention, in the second aspect of the present invention, the outer peripheral surface of the piston for the internal combustion engine is subjected to shot peening as a surface treatment.

According to a fourth aspect of the present invention, in the second aspect of the present invention, the inner peripheral surface of the piston pin hole of the piston for the internal combustion engine is subjected to a lubricant impregnated hard anodic oxide film treatment as a surface treatment. .

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a side view of the piston for an internal combustion engine according to the present invention, FIG. 2 is a front view of the piston for the internal combustion engine (a view in the direction of arrow A in FIG. 1), and FIG. Line sectional view, FIG.
FIG. 4 is a sectional view taken along line CC of FIG. 3.

The piston 1 according to the present embodiment is for a two-stroke engine. As shown in FIG. 4, the skirt portion 1a is formed thinner than the top portion 1b, and the inner peripheral wall of the skirt portion 1a faces each other. As shown in FIGS. 3 and 4, a thick pin boss portion 1c is integrally formed at the position where the pin boss 1c protrudes.
A piston pin hole 2 for fitting and holding a piston pin (not shown) is coaxially formed in each pin boss 1c.

A piston ring groove 3 for fitting and holding a piston ring (not shown) is formed on the outer periphery of the upper part of the piston 1.
Are formed over the entire circumference.

The piston 1 having the above-described structure is integrally formed by forging, and a small connecting rod (not shown) is fitted by a piston pin (not shown) fitted and held in a piston pin hole 2 formed in the pin boss 1c. Connected to the end,
It is slidably fitted to a cylinder (not shown) via a piston ring (not shown) fitted in a piston ring groove 3 formed on the upper outer periphery. The piston 1 is connected to a crankshaft (not shown) via a connecting rod, and the reciprocating motion of the piston 1 in the cylinder is converted by the connecting rod into rotational motion of the crankshaft.

By the way, the piston 1 according to the present embodiment
Is made of a low Si content aluminum alloy having a Si content of less than 10%, and has been subjected to a surface treatment to enhance abrasion resistance and galling resistance at necessary portions.

As described above, in this embodiment, 10 to 20
% Of Si instead of the conventional high Si-containing material, the fatigue strength and tensile strength (particularly high-temperature strength) of the high Si-containing material
Since the low Si content aluminum alloy having high toughness and high toughness is selected as the material of the piston 1, the thickness of the piston 1 can be reduced in design, and the weight of the piston 1 can be reduced to reduce engine vibration and improve engine performance. Can be realized.

On the lower surface of a piston ring groove formed on a conventional piston made of a material having a high Si content, a large number of primary crystals are projected from the lower surface of the piston ring groove.
Since the creep states of the portions are different, the combustion pressure is repeatedly received via the piston ring during use, and the surface is likely to be uneven, and the ring sealability is likely to be reduced.

On the other hand, the aluminum alloy having a low Si content is uniform in material, and the lower surface of the piston ring groove 3 formed in the piston 1 according to the present embodiment does not become uneven, but is high. In addition to ensuring the sealing performance, the heat conductivity of the aluminum alloy having a low Si content is higher than that of the conventional material having a high Si content, so that the heat transfer from the piston 1 through the piston ring to the cylinder is efficiently performed. The heat radiation of the piston 1 is improved. Therefore, the temperature of the piston 1 according to the present invention can be suppressed to be lower than that of the piston having a high Si content,
Combined with the high-temperature strength of the contained material, the piston 1 according to the present invention can be further thinned and lightened.

As described above, by selecting a low Si content aluminum alloy as the material of the piston 1,
The strength, heat dissipation and toughness of the piston 1 can be increased to reduce the thickness and weight. However, for the wear resistance and galling resistance, a suitable surface treatment according to the function is applied to the parts where these are required. This solved the problem.

In the piston 1, parts requiring wear resistance and galling resistance are the outer peripheral surface of the skirt portion 1a (the sliding surface with the cylinder), the inner peripheral surface of the piston pin hole 2, and the lower surface of the piston ring groove 3. In the present embodiment, the following surface treatment is performed on these portions according to the functions.

Outer peripheral surface of skirt portion 1a (sliding surface with cylinder): The outer peripheral surface of skirt portion 1a (sliding surface with cylinder) is subjected to shot peening under a specific condition to prevent the outer peripheral surface from becoming uneven. Since the regular unevenness is formed, the unevenness holds the lubricant and enhances the lubricity of the outer peripheral surface, and the surface becomes hard to seize. As a result, the outer peripheral surface of the skirt portion 1a has abrasion resistance. Properties and galling resistance can be improved. At the time of shot peening, the piston pin hole 2 and the piston ring groove 3
Is masked.

Incidentally, a thin hard film treatment such as ion plating may be performed on the outer peripheral surface subjected to the shot peening.

Inner peripheral surface of piston pin hole 2: By subjecting the inner peripheral surface of piston pin hole 2 to a surface treatment such as a hardened anodic oxide film treatment impregnated with a lubricant, the inner peripheral surface can be sufficiently worn for practical use. Properties and galling resistance can be ensured.

The lower surface of the piston ring groove 3: The piston ring groove 3 can be subjected to a thin surface treatment that does not impede heat conduction. Since it is high and has high creep resistance, it can withstand use even if untreated.

Therefore, as in the present embodiment, a low Si content aluminum alloy having a Si content of less than 10% is selected as a material of the piston 1 and a suitable surface treatment corresponding to each function is performed at a necessary portion. By applying the method described above, it is possible to reduce the thickness and weight of the piston 1 by increasing the strength, heat dissipation, and toughness while securing the same wear resistance and galling resistance of the piston 1 as before.

Although the present invention has been described with reference to the embodiment in which the present invention is particularly applied to a piston for a two-cycle engine, it is needless to say that the present invention is similarly applicable to a piston for a four-cycle engine. Further, in the above embodiment, the case where the present invention is applied to a piston integrally formed by forging has been described. However, the present invention is similarly applicable to a piston formed by casting or total cutting. is there.

[0028]

As is apparent from the above description, according to the present invention, the piston for an internal combustion engine is made of a low Si content aluminum alloy having a Si content of less than 10%, which has abrasion resistance and resistance to wear. Since the surface treatment for enhancing the galling property has been performed, it is possible to reduce the thickness and weight of the piston by increasing the strength, heat dissipation and toughness while securing the same wear resistance and galling resistance as the conventional piston. The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a side view of an internal combustion engine piston according to the present invention.

FIG. 2 is a front view (a view in the direction of arrow A in FIG. 1) of the piston for an internal combustion engine according to the present invention.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a sectional view taken along line CC of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal-combustion engine piston 1a Skirt part 1b Top part 1c Pin boss part 2 Piston pin hole 3 Piston ring groove

Claims (4)

[Claims] 1. A piston for an internal combustion engine, comprising a low Si content aluminum alloy having a Si content of less than 10% and subjected to a surface treatment for enhancing abrasion resistance and galling resistance. 2. The piston for an internal combustion engine according to claim 1, wherein said surface treatment is performed on an outer peripheral surface and an inner peripheral surface of a piston pin hole. 3. The piston for an internal combustion engine according to claim 2, wherein shot peening is performed on the outer peripheral surface as a surface treatment. 4. A piston for an internal combustion engine according to claim 2, wherein the inner peripheral surface of the piston pin hole is subjected to a lubricant impregnated hard anodic oxide film treatment as a surface treatment.