A piston with a cooling cavity adjacent to piston-ring grooves

Abstract

 A piston (1) has a cooling cavity (3) adjacent to piston-ring grooves (2). A portion of the piston (1), lying between the edge of the piston-ring groove and the edge of the cooling cavity, is strengthened with a composite material (4). The volumetric ratio of a porous metal (4a) incorporated in the composite material (4) varies from the edge of the piston-ring groove to the edge of the cooling cavity (3). Thus, not only the strength of the piston but also the wear resistance of the piston-ring groove is much improved.

Description

[0001] This invention relates to an improved piston with a cooling cavity adjacent to piston-ring grooves.

[0002] Japanese Patent Publication No. 60-25619 and Japanese Laid Open Patent No. 62-131771 disclose respective aluminum-alloy composite materials made in such a way that the molten aluminum alloy is penetrated into the porous metal under a high pressure so as to improve the mechanical strength thereof.

[0003] Moreover, Japanese Laid Open Patent No. 59-21393, Japanese Laid Open Patent No. 59-218341 and Japanese Laid Open Patent No. 59-212159 disclose respective compound layers of the porous metal of iron, nickel or copper with the aluminum alloy so as to improve the wear resistance of the aluminum alloy.

[0004] When such composite material, in which the porous metal is incorporated, is applied to a required portion, such as a portion of a piston, the strength and the wear resistance of the piston and the like will be improved.

[0005] However, between the above mechanical properties, there is an opposition of one property to the other in relation with the volumetric ratio of the porous metal, so that if the volumetric ratio is designed to be more than 60%, for instance, the wear resistance of the piston-ring groove will be improved, but the mechanical strength will be apt to reduce, for example, due to separation initiated in the interface between the porous metal, and the metal (e.g. aluminum) penetrated in the porous metal.

[0006] That is, the higher the volumetric ratio is, the larger the wear resistance is, but the smaller the strength of the interface is. Conversely, the lower the volumetric ratio is, the larger the strength of the interface is, but the smaller the wear resistance is.

[0007] In accordance with the invention, in a piston with a cooling cavity adjacent to piston-ring grooves, a portion of the piston, lying between a partial edge of at least a top piston-ring groove and a partial edge of the cooling cavity which is in opposed relation to the former partial edge, is strengthened with a composite material, and a volumetric ratio of a porous metal, incorporated in the composite material, is changed in accordance with the shift of position from the partial edge of the piston-ring groove to that of the cooling cavity.

[0008] In preferred embodiments of this invention, the porous metal is made of a Ni-Cr base metal. The volumetric ratio is within a range of 8-70% in a part near to the piston-ring groove, and within a range of 0.5-5% in a part near to the cooling cavity.

[0009] Moreover, the porous metal lying between the edge of the piston-ring groove and that of the cooling cavity is made by superposed layers, each of which has a different volumetric ratio from the rest.

[0010] A non-limiting embodiment of the present invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a front view, half broken away and in section, of a piston according to an embodiment of this invention;

Figure 2 is an enlarged fragmentary sectional view illustrating a portion of the piston of Figure 1;

Figure 3A is a sectional view of an annularly formed porous metal to be embedded in the piston of Figure 1; and

Figure 3B is a plan view of the annularly formed porous metal of Figure 3A.

[0011] Referring to the drawings in detail, and initially to figure 1 thereof, it will be seen that a piston embodying the present invention has a cooling cavity 3 adjacent to piston grooves 2.

[0012] The cooling cavity 3 communicates by passages (not shown) with the inside of the piston 1, so that oil flowing from the crank case to the cooling cavity 3 inhibits an increase of temperature of the piston 1.

[0013] As shown in Figure 2, the piston 1 is reinforced by a composite material 4 from a partial edge of a top piston-ring groove 2 to a partial edge of the cooling cavity 3, which is in opposed relation to the partial edge of the top piston-ring groove 2.

[0014] As shown in Figure 3B, a porous metal 4a incorporated in the composite material 4 is of annular shape, and, as shown in Figure 3A, a part, denoted by numeral 5, of a sectional profile coincides with a curve, which forms a part of the periphery of the cooling cavity 3.

[0015] It will be seen from Figure 3A that the porous metal 4a is made by superposed layers, each of which has a different volumetric ratio Vf from the rest. That is, the porous metal 4a comprises the outermost layer 6, which is to be located near to the piston-ring groove 2 and the volumetric ratio Vf of which is in a range of 8-70%; the innermost layer 7, which is to be located near to the cooling cavity 3 and the volumetric ratio Vf of which is within a range of 0.5-5%; and the intermediate layer 8, which is interposed between the outermost layer 6 and the innermost layer 7 and the volumetric ratio Vf of which is smaller than that of the uppermost layer 6 and larger than that of the innermost layer 7. It is noted that the intermediate layer 8 is in a single layer, but may be in plural layers. If the intermediate layer 8 is in plural layers, the volumetric ratio Vf will be changed stepwise from the outside to the inside of the plural layers.

[0016] The porous metal 4a is made of Ni-Cr base metal, and chromium therein is in a range of 10-100%. Further, the innermost layer 7 may be made of Ni, and a predetermined amount of chromium may be included, for example, by means of treating the porous metal 4a by chromizing.

[0017] The piston 1 is manufactured as follows.

[0018] Firstly, the ring-shaped porous metal 4a is set in a predetermined position of a permanent mold, together with a core for the cooling cavity 3, and the like. A molten aluminum alloy of AC8A is poured into the permanent mold at a temperature of 760°C, and solidified under high pressure of 800 kg/cm². Thereafter, the piston-ring groove and the like are formed by machining.

[0019] Having described an illustrative embodiment of this invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the invention. For example, the porous metal was made, in the embodiment, by the superposed layers, but may be made en bloc. In that event, the volumetric ratio Vf will be changed not stepwise but continuously.

[0020] The embodiment shown in the drawings provides a piston which avoids the previously described problems associated with the prior art. It has a volumetric ratio of a porous metal incorporated in a composite material, which is applied to the piston, which is larger in a part near to a piston-ring groove, and smaller in a part near to a cooling cavity, which is provided adjacent to the piston-ring groove, so that, if the piston-ring groove comes in severe sliding contact with a piston ring, the piston-ring groove having a good wear resistance will scarcely be damaged. Furthermore, the strength of the piston will be much improved due to an improved strength of the interface of the composite material near to the cooling cavity.

Claims

1. A piston (1) with a cooling cavity (3) adjacent to piston-ring grooves (2) wherein a portion thereof, lying between a first edge portion of at least a top piston-ring groove and a second edge portion of the cooling cavity (3) which is in opposed relation to the first edge portion, is strengthened with a composite material (4), and the volumetric ratio of a porous metal (4a) incorporated in the composite material varies from the first edge portion to the second edge portion.

2. A piston according to claim 1, wherein the porous metal (4a) is made of a Ni-Cr base metal.

3. A piston according to claim 1 or 2, wherein the volumetric ratio is within a range of 8 - 70% in a part (6) near to the piston-ring groove, and within a range of 0.5 - 5% in a part (7) near to the cooling cavity (3).

4. A piston according to any one of claims 1 to 3, wherein the porous metal (4a) lying between the first edge portion and the second edge portion comprises superposed layers, each of which has a different volumetric ratio from the others.

Drawing