JPH0133809Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a piston for an internal combustion engine.

Some internal combustion engines have cylinder blocks made of high-silicon aluminum alloy and pistons made of aluminum alloy to reduce weight. In this type of internal combustion engine, the cylinder bore and piston are made of the same material.
In particular, scuffing may occur on the sliding surface with the piston skirt.

As a measure against this scuffing, some piston skirts have been plated with iron in the past, but this has not been able to completely prevent scuffing. In other words, iron plating is hard, and even if the surface of the iron plating has a rough surface, it will not blend in easily.Therefore, if it slides against the cylinder bore on the rough surface, an oil film will break and the cylinder bore sliding surface will be damaged, so avoid scuffing. It could not be completely prevented.

In addition to this, various methods have been proposed in which the wear resistance of the piston is improved by plating the surface of the piston with various metals or forming a metal layer (for example, No. 78856, 1987-
No. 2239, Utility Model Application Publication No. 55-20695, etc.), none of which have the structure of the present invention described below.

The purpose of the present invention is to more completely prevent the occurrence of scuffing in an internal combustion engine equipped with a high-silicon aluminum alloy cylinder bore wall and an aluminum alloy piston. It provides:

In order to achieve this purpose, in the internal combustion engine piston of the present invention, the cylinder block is made of a high-silicon aluminum alloy, the piston is made of an aluminum alloy, and the surface of the piston skirt is made of iron. A lead-tin alloy plating is applied on top of the plating. In this case, regarding the iron plating, it is possible to first apply nickel plating to the surface of the piston skirt to prevent the iron plating from peeling off, and then apply iron plating on top of that, and the present invention also applies to such cases. It includes.

Iron-based plating is 100% Fe iron plating, and it is lead-free.
It may be an alloy consisting only of tin, or it may be 0.5
It may be an iron-phosphorus alloy plating containing % to 15% P. Furthermore, lead-tin alloy plating is 5% to 15%
It may be a lead-tin alloy containing % tin and the remainder lead;
It may be a lead-tin alloy containing 10% or less of copper (Cu) or the like.

In pistons with iron plating and lead-tin alloy plating, the lead-tin alloy is soft, so even if there are microscopic irregularities on the surface of the lead-tin alloy, the sliding movement with the cylinder bore will be smooth. Often, initial run-in is significantly improved. In addition, over repeated use, lead-tin alloy plating wears out and the iron plating becomes exposed on the surface, but even if the convex parts of the iron plating begin to be exposed first, the Because it is exposed, that part undergoes more wear than if the entire iron plating were exposed at once, and the protrusion comes off smoothly, which greatly improves the compatibility between the iron plating and the cylinder bore. As the exposure of the plating progresses, further progress of wear on the piston is suppressed, so wear resistance is also maintained at a good level. That is, through improved conformability, sliding properties, seizure resistance, and scuffing prevention performance are improved, and wear resistance is also improved due to the exposure of the iron-based plating.

The thickness of the iron-based plating is preferably about 20μ or less, and the thickness of the lead-tin plating is preferably about 2μ to 20μ. This is because if the iron-based plating exceeds 20μ, there is a risk of the plating layer peeling off, and if the lead-tin plating is less than 2μ, the unevenness of the iron-based plating will appear on the surface and interfere with the cylinder bore. This is because the initial integration is not good and the lead-tin plating layer cannot be plated uniformly, and if the lead-tin plating exceeds 20μ, the lead-tin plating layer is a soft layer and may be peeled off at any time. be.

Hereinafter, preferred embodiments of the piston for internal combustion engines of the present invention will be described with reference to the drawings.

FIG. 1 shows a structure near a piston and cylinder bore of an internal combustion engine according to an embodiment of the present invention. In the figure, 1 is a cylinder bore, 2 is a piston, and the piston 2 slides within the cylinder bore 1.
Further, 3 and 4 are piston rings consisting of compression rings, and 5 is an oil ring. Normally, the diameter of the piston 2 is gradually reduced as it goes above the oil ring 5 part, although it is slightly reduced. 6 makes sliding contact with the cylinder bore 1.

To reduce the weight of the engine, the inner surface of cylinder bore 1 is made of high-silicon aluminum alloy, such as 17Si-
4Cu−0.5Mg−Bal Al, and the piston 2 is made of aluminum alloy, such as JIS AC8A−
Consists of T6 equivalent. And piston 2
As shown in FIG. 2, two plating layers are formed on the surface of the piston skirt portion 6: an iron plating 7 and a lead-tin alloy plating 8 thereon. The layer of iron-based plating 7 is made of 100% Fe plating, for example, and its thickness is 20 μm or less. Furthermore, the layer of lead-tin alloy plating 8 has a thickness of 2μ to 20μ.
As an example, it is made of 10% Sn-BalPb with a thickness of 10μ.

When forming the layer of iron plating 7, in order to more completely prevent the iron plating 7 from peeling off, nickel (Ni) is applied to the surface of the piston skirt portion 6 in advance.
Plating may be applied and then iron plating 7 may be applied thereon, and the present invention also includes such a case.

The iron-based plating 7 and the lead-tin alloy plating 8 are applied over the entire outer peripheral surface of the piston skirt portion 6, that is, the sliding surface of the piston skirt portion 6 with the cylinder bore 1.

Next, the effects of the piston of the above embodiment configured as described above will be explained.

FIG. 3 shows the durability test results of the piston of the above example in comparison with a conventional piston. The durability test was conducted using a 2000 c.c. four-cylinder gasoline engine, running at 5500 rpm, full load, and for 50 hours. In Figure 3, the case of a piston without conventional plating is designated as A, the case of A with only iron plating applied to the piston is designated as B,
The case where iron-based plating and lead-tin plating according to the present invention are applied is designated as C, and A, B, and C are plotted on the horizontal axis. Furthermore, the depth of surface roughness of the piston skirt portion 6 is plotted in units of μ on the vertical axis. The larger the surface roughness depth is, the more scuffing phenomenon occurs.

As is clear from Fig. 3 showing the test results, in the conventional case A, a surface roughness depth of 20 μ or more occurs, resulting in scuffing, and in the case of iron plating only, B also has a rough surface depth of 20 μ or more compared to case A. It can be seen that although the scuffing is suppressed, there is still considerable surface roughness. In case B, considerable surface roughness occurs not only on the piston skirt portion 6 but also on the cylinder bore 1 side. However, in case C of the present invention,
The surface roughness depth is 10μ or less, and in this state, the lead-tin alloy plating 8 on the outermost surface is still left, although it has progressed to wear, and in this state, a part of the iron-based plating 7 begins to be exposed. This shows that the progress of wear suddenly stops in this state. Note that the surface roughness of cylinder bore 1 is B when the cylinder is plated with iron.
was significantly suppressed compared to

The reason why such good results can be obtained is that the lead-tin alloy plating 7 is a very compatible material that can be used as a bearing metal material, and has a hardness of about 5 to 20 on the Vickers hardness Hv. It is possible to fit the cylinder bore 1 of the mating member during sliding without damaging it. Even if the lead-tin alloy plating 7 gradually wears away and the uneven tips of the iron-based plating 8 are exposed, the iron-based plating 8 has a Vickers hardness of Hv.
Although it is hard with a hardness of 200 to 400, as it is exposed locally, that part is worn smoothly by sliding, and the corners are smoothed out. That is, the piston skirt portion 6 and the cylinder bore 1 are worn smoothly without damaging them, and surface roughness and scuffing are suppressed. Then, as the wear progresses further and the degree of exposure of the iron-based plating 8 increases, the progress of the wear is eventually sufficiently suppressed by the action of the iron-based plating 8.

As described above, when using the internal combustion engine piston of the present invention, the wear resistance of the piston is improved by applying two layers of iron plating and lead-tin alloy plating to the piston skirt. By improving the initial fit with the cylinder bore while maintaining the same piston condition as previously applied, it is possible to prevent scuffing from occurring.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a piston for an internal combustion engine according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the piston skirt surface of the piston of FIG. FIG. 3 is a characteristic diagram related to the durability of a piston. 1... Cylinder bore, 2... Piston, 5...
Oil ring, 6... Piston skirt part, 7...
...Iron-based plating, 8...Lead-tin alloy plating.

Claims (1)

[Claims for Utility Model Registration] (1) In an internal combustion engine equipped with a cylinder bore made of high silicon aluminum alloy and a piston made of aluminum alloy, iron plating is applied to the skirt portion of the piston, and an additional 5% A piston for an internal combustion engine characterized by being plated with a lead-tin alloy containing ~15% tin and the remainder being lead. (2) The piston for an internal combustion engine according to claim 1, wherein the iron plating is made of 100% iron plating. (3) The piston for an internal combustion engine according to claim 1, wherein the iron-based plating is an iron-phosphorus alloy plating containing 0.5% to 15% phosphorus. (4) The piston for an internal combustion engine according to claim 1, wherein the lead-tin alloy plating is made of an alloy of only lead and tin. (5) The piston for an internal combustion engine according to claim 1, wherein the lead-tin alloy plating comprises a lead-tin alloy plating containing 10% or less of at least one of Zn, In, and Cu. (6) The piston for an internal combustion engine according to claim 1, wherein the lead-tin alloy plating has a thickness of 2μ to 20μ.