WO2008059330A1

WO2008059330A1 - Cylinder block and method for producing cylinder block

Info

Publication number: WO2008059330A1
Application number: PCT/IB2007/003279
Authority: WO
Inventors: Thoshihiro Takami
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-11-17
Filing date: 2007-10-30
Publication date: 2008-05-22
Also published as: JP2008128054A; JP4329810B2

Abstract

In an open-deck cylinder block 1 with a cylinder liner 3 incorporated therein, a MMC ring 4, which is made of a metal matrix composite body and which has a short cylinder shape, is closely fitted on the outer periphery of the cylinder liner 3, and the outer periphery of the MMC ring 4 faces a water jacket 12, only at a deck-face portion. Thus, a layer made only from an aluminum alloy is not formed in the deck-face portion. As a result, the deck-face portion has a higher strength.

Description

CYLINDER BLOCKAND METHOD FOR PRODUCING CYLINDER BLOCK

BACKGROUND OFTHE INVENTION

1. Field of the Invention [0001] The invention relates generally to a cylinder block used in an internal combustion engine, for example, an engine for an automobile, and a method for producing such cylinder block. More specifically, the invention relates to a technology for enhancing the strength of a deck-face (top-face) portion of a cylinder block.

2. Description of the Related Art [0002] Cylinder blocks for automobile engines, which are made from an aluminum alloy, have come into widespread use to meet the demand for lighter-weight cylinder blocks.

[0003] Cylinder blocks are usually produced by casting. In many cases, the die-casting method is employed to produce cylinder blocks to ensure a high accuracy of the cylinder blocks and to reduce production time. The above-mentioned aluminum-alloy cylinder blocks are usually cast with cylinder liners incorporated therein. The cylinder liners are members made, for example, from cast-iron, and used to form cylinder bore walls. The cylinder liners are incorporated within the cylinder blocks to ensure sufficient mechanical strength, abrasion resistance, thermal resistance, etc. of the cylinder bore walls along which pistons of an engine slide (refer, for example, to Japanese Patent Application Publication No. 07-284905 (JP-A-07-284905)).

[0004] Cylinder blocks may be classified as an open-deck or a closed-deck based on the shape of the block. In an open-deck cylinder block, a water jacket, used as a coolant passage formed within the cylinder block, opens on the top face of the cylinder block (the face on which a cylinder head is fitted, namely, the deck-face). In a closed-deck cylinder block, a water jacket does not open on the top face of the cylinder block. The open-deck cylinder blocks are more suitable for the die-casting method, because producing the open-deck cylinder block does not require a core to form the water jacket. [0005] Recently, obtaining a higher pressure in a cylinder (hereinafter, referred to as a "cylinder pressure") in the power stroke has been demanded in order to obtain greater power from an engine. The cylinder pressure of a diesel engine (generally, approximately 16 MPa) is higher than that of a gasoline engine. Accordingly, the cylinder block for a diesel engine needs to be provided with a higher strength in order to withstand the cylinder pressure increased to obtain greater power from the engine.

[0006] However, when the above-described aluminum-alloy cylinder block is produced by the die-casting method, casting defects, described below in detail, may be caused, and a defective portion of the cylinder block may fail to possess a sufficient strength to withstand the increased cylinder pressure.

[0007] According to the die-casting method, a molten aluminum alloy is compressed and then poured into a cavity formed within a die. Accordingly, air is sent to the cavity along with the molten aluminum alloy. If the aluminum alloy is cooled with air-bubbles left therein and then solidified, such air-bubbles cause cast cavities. Also, because the molten aluminum alloy is temporarily stored in an injection sleeve, aluminum-alloy oxide films are frequently formed on the surface of the molten aluminum alloy stored in the injection sleeve. Then, such oxide films may be sent along with the molten aluminum alloy to the cavity of the die. If the aluminum alloy is cooled with the oxide films included therein and then solidified, a portion of the cylinder block, in which the oxide films are left, becomes a defective portion. The defective portion having such cast cavities and/or oxide films is lower in strength than the portions that do not have any casting defects.

[0008] There is a metal matrix composite (hereinafter, referred to as a "MMC") that is formed by combining different types of materials together so as to be provided with an enhanced strength. For example, Japanese Patent Application Publication No. 63-19050

(JP-A-63- 19050) and Japanese Patent Application Publication No. 10-220278

(JP-A-10-220278) each describe a technology for using a MMC to form a cylinder block.

[0009] According to JP-A-63- 19050, two annular projections are formed on the outer periphery of a cylinder liner, and a cylinder block is cast with a reinforcing fiber-bundle preform, which is made from alumina, arranged between these annular projections. In this way, the cylinder liner and the reinforcing fiber-bundle are incorporated within the cylinder block in the casting process. With this structure, expansion of the cylinder liner toward a cylinder head is suppressed by the reinforcing fiber-bundle. [0010] According to JP-A- 10-220278, a rib is formed by reducing the thickness of the upper-end portion (the deck-face-side end portion) of a cylinder liner, and an inorganic fiber compact is fitted, under pressure, around the outer periphery of the rib. After the cylinder liner and the inorganic fiber compact are incorporated within a cylinder block, the top face of the cylinder block is machined to form the deck-face, and the inner periphery of the cylinder liner is machined to form the cylinder bore walls. When the inner periphery of the cylinder liner is machined, the rib formed at the upper-end portion of the cylinder liner is removed together with the inner peripheral portion of the inorganic fiber compact to expose the inorganic fiber compact, which has become a MMC, into the bore. [0011] The cylinder block needs to be provided with a sufficient strength to withstand a cylinder pressure in the power stroke of the engine. More specifically, because a considerably high stress is applied to a portion that undergoes application of a cylinder pressure (combustion pressure) achieved at the early stage of the power stroke at which the cylinder pressure is maximized (for example, a cylinder pressure achieved when a crankshaft is rotated by a crank angle of ten and several degrees from a rotational position at which a piston reaches the top dead center), namely, a cylinder head-side portion of the cylinder block (the upper portion of a cylinder block, in an engine in which the axis of a cylinder extends substantially vertically), this portion needs to be provided with a particularly high strength. Especially, in the above-described open-deck cylinder block, a high stress is applied to the cylinder bore wall which is located on the inner side of the water jacket. Accordingly, a sufficient strength needs to be provided to suppress deformation of the cylinder head-side portion of the cylinder bore wall portion (the upper-end portion of the cylinder block). In the meantime, however, the cylinder bore wall portion should be thin in order to be efficiently cooled. The cylinder bore wall portion, especially, the cylinder head-side portion of the cylinder bore wall portion needs to be both thin and sufficiently strong.

[0012] In the cylinder block described in JP-A-63- 19050, however, the reinforcing fiber-bundle preform is not provided at the upper-end portion of the cylinder liner. In other words, the reinforcing preform is not arranged at the portion that should be provided with the highest strength (the upper-end portion of the cylinder block). Not only that, because the material of a cylinder block body (for example, the aluminum alloy) is poured, in the form of molten metal, into a space around the reinforcing preform, casting defects caused due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy, may be present in the upper-end portion of the cylinder block. In this case, the strength of this defective portion may be insufficient.

[0013] In the cylinder block described in JP-A-10-220278, the inorganic fiber compact, which has become the MMC, is exposed into the bore, at the deck-face portion, as described above. Namely, in the cylinder block described in JP-A-10-220278, the inorganic fiber compact, which has become the MMC, is arranged at the portion that needs to be provided with the highest strength (the upper-end portion of the cylinder block). However, the material of the cylinder block body (the aluminum alloy) is poured, in the form of molten metal, into the space around the inorganic fiber compact. In this case as well, casting defects caused due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy, may be present in the upper-end portion of the cylinder block. In this case, the strength of this defective portion may be insufficient.

[0014] In the cylinder block described in JP-A-10-220278, because the rib of the cylinder liner is removed as described above, the inorganic fiber compact, which has become the MMC, and the cylinder liner contact each other only at the tip-face portion of the cylinder liner, and, therefore, the inorganic fiber compact and the cylinder liner are not in close contact with each other. Especially, because the portion at which the inorganic fiber compact and the cylinder liner contact each other is positioned at the upper-end portion of the cylinder block, of which the temperature becomes high in the power stroke, the inorganic fiber compact may be separated from the tip-end face of the cylinder liner due to a difference in the expansion rate between the materials of the inorganic fiber compact and cylinder liner. Such separation may cause cracking in a portion of the cylinder block body, which is positioned on the outer peripheral side of the inorganic fiber compact.

[0015] Further, in the cylinder block described in JP-A- 10-220278, when the inner periphery of the cylinder liner is machined, the inner periphery of the inorganic fiber compact need to be machined as well, which makes it difficult to ensure high accuracy of the cylinder block. Unlike a cylinder block in which the cylinder bore wall portion is formed of a single material (for example, cast-iron), the faces formed of two types of materials that are different in machining characteristics need to be machined such that smooth faces with no level difference therebetween is formed. However, performing such machining process is difficult. It is, therefore, difficult to select the machining method and machining tools. Accordingly, it is not easy to translate the technology described in JP-A- 10-220278 into practical applications.

SUMMARY OF THE INVENTION

[0016] The invention provides an open-deck cylinder block in which a deck-face portion of the cylinder block is provided with a high strength while a cylinder liner and a metal matrix composite are reliably kept in close contact with each other in the deck-face portion. The invention also provides a method for producing such cylinder block.

[0017] The invention relates to an open-deck cylinder block in which a cylinder bore wall is formed by a cylinder liner. In a deck-face portion (that includes a deck-face of the cylinder block, on which a cylinder head is fitted, and a portion near the deck-face) of the cylinder block, a MMC (metal matrix composite) is closely fitted on the outer periphery of the cylinder liner. The outer periphery of the MMC faces a water jacket. A layer made only from the material of a cylinder block body (for example, an aluminum alloy) is not formed in a portion of the deck-face portion, which is on the inner side of the water jacket.

[0018] A first aspect of the invention relates to an open-deck cylinder block which is cast with a cylinder liner, used to form the cylinder bore wall, incorporated within the cylinder block, and in which a water jacket opens on a deck-face. In the cylinder block, a metal matrix composite body that is formed by impregnating a cylindrical porous body with a cylinder block material is fitted on the outer periphery of the cylinder liner at a deck-face portion of the cylinder block. The length of the porous body in the axial direction thereof is shorter than the length of the cylinder liner in the axial direction thereof. The outer periphery of the metal matrix composite body faces the water jacket, and the entire inner periphery of the metal matrix composite body is kept in close contact with the outer periphery of the cylinder liner. The inner periphery of the cylinder liner faces the cylinder bore.

[0019] A second aspect of the invention relates to an open-deck cylinder block which is cast with a cylinder liner, used to form the cylinder bore wall, incorporated within the cylinder block, and in which a water jacket opens on a deck-face. The casting process is performed with a cylindrical porous body fitted on the outer periphery of the cylinder liner at a deck-face portion of the cylinder block. The length of the porous body in the axial direction thereof is shorter than the length of the cylinder liner in the axial direction thereof. As a result, only the cylinder liner and a metal matrix composite body formed by impregnating the porous body with a cylinder block material are present between the cylinder bore and the water jacket, at the deck-face portion of the cylinder block.

[0020] According to each of the first and second aspects of the invention, only the cylinder liner and the metal matrix composite body made from a metal matrix composite are present in a portion of the deck-face portion on which the cylinder head is fitted and which should be provided with the highest strength in the cylinder block, the portion being on the inner side of the water jacket. Accordingly, this portion is free of a layer (the cylinder block material which has not become a MMC) made only from the cylinder block material (for example, an aluminum alloy). Namely, in the casting process, air-bubbles and oxide films that are carried toward the deck-face portion are trapped in the porous body, and such air-bubbles and oxide films are prevented from being carried into the deck-face portion. Accordingly, casting defects due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material, are not caused in the deck-face portion of the cylinder block. As a result, the deck-face portion is provided with a sufficient strength. In addition, the entire inner periphery of the metal matrix composite body is kept in close contact with the outer periphery of the cylinder liner. Accordingly, it is possible to stably maintain such close contact between the metal matrix composite body and the cylinder liner over long periods. [0021] In each of the above-described aspects of the invention, the porous body may be fitted, under pressure, on the outer periphery of the cylinder liner, and then the porous body may be impregnated with the cylinder block material, whereby the metal matrix composite body is formed. In this way, the casting process is performed when there is no clearance between the porous body and the cylinder liner. Namely, a layer (the cylinder block material which has not become the MMC) made only from the cylinder block material (for example, an aluminum alloy) is not formed between the porous body and the cylinder liner. As a result, it is possible to reliably prevent casting defects due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material from being caused between the porous body and the cylinder liner.

[0022] In each of the above-described aspects of the invention, the metal matrix composite body may be formed by impregnating the porous body with the cylinder block material that flows, in the form of molten metal, in the axial direction of the cylinder liner, and the face of the porous body, through which the cylinder block material in the form of molten metal flows into the porous body, may be sloped such that the cylinder liner-side end of the face is positioned downstream of the water jacket-side end of the face in the direction in .which the cylinder block material in the form of molten metal flows.

[0023] With this structure, when the molten metal (the cylinder block material) is poured into the die and then flows through the cavity toward the inside portion of the porous body, the air-bubbles and/or foreign matter (for example, aluminum-alloy oxide films) contained in the cylinder block material are carried toward the inner periphery of the porous body and accumulated near the inner periphery of the porous body. Accordingly, after the cylinder block material is cooled and solidified, the outer peripheral-side portion (the water jacket-side portion) of the metal portion that faces the lower-end face of the porous body is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material. A stress of the cylinder pressure in the power stroke of the engine is largely applied to the outer peripheral-side portion (water jacket-side portion) of the cylinder barrel between the cylinder bore and the water jacket. However, the outer peripheral-side portion to which such large stress is applied is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material. Accordingly, this portion is provided with a sufficient strength. As a result, it is possible to improve the reliability of the cylinder block.

[0024] In each of the above-described aspects of the invention, the metal matrix composite body may be formed by impregnating the porous body with the cylinder block material that flows, in the form of molten metal, in the axial direction of the cylinder liner, and the face of the porous body, through which the cylinder block material in the form of molten metal flows into the porous body, may have a recess at the center between the cylinder liner-side end of the face and the water jacket-side end of the face.

[0025] With this structure, when the cylinder block material is poured into the die and then flows through the cavity toward the inside portion of the porous body, the air-bubbles and/or foreign matter contained in the cylinder block material are carried toward the recess formed in the face of the porous body and accumulated in the recess. Accordingly, after the cylinder block material is cooled and solidified, the outer peripheral-side portion (the water jacket-side portion) of the cylinder block material portion that faces the face (for example, the lower end face) of the porous body is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material. As described above, a stress of the cylinder pressure in the power stroke of the engine is largely applied to the outer peripheral-side portion of the cylinder barrel. However, the outer peripheral-side portion to which such large stress is applied is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material. Accordingly, this portion is provided with a sufficient strength. As a result, it is possible to improve the reliability of the cylinder block.

[0026] In each of the above-described aspects of the invention, the porous body before being fitted on the outer periphery of the cylinder liner may be shaped such that the inner diameter of a portion of the porous body, which is proximal to the deck-face, is smaller than the inner diameter of a portion of the porous body, which is distal to the deck-face.

[0027] Setting the inner diameters of the porous body in this manner facilitates the process of fitting the cylinder liner into the porous body under pressure. In addition, after the cylinder liner is fitted into the porous body, no clearance is left between the porous body and the cylinder liner. Accordingly, a layer made only from the material of the cylinder block (for example, an aluminum alloy) is not formed between the porous body and the cylinder liner. Therefore, it is possible to reliably prevent casting defects due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material from being caused between the porous body and the cylinder liner.

[0028] In each of the above-described aspects of the invention, the porous body before dies are clamped together may be shaped such that the outer diameter of a portion of the porous body, which is proximal to the deck-face, is smaller than the outer diameter of a portion of the porous body, which is distal to the deck-face.

[0029] According to each of the above-described aspects of the invention, the outer periphery of the metal matrix composite body faces the water jacket. Accordingly, when the dies are clamped together in the casting process, a water jacket forming die is fitted to substantially the entire outer periphery of the porous body. In this case, setting the outer diameters of the porous body in the above-described manner facilitates the process of fitting the water jacket forming die from the deck-face side of the porous body. In addition, when the dies are clamped together, no clearance is left between the outer periphery of the porous body and the water jacket forming die. Accordingly, it is possible to prevent the cylinder block material (for example, an aluminum alloy) in the form of molten metal from entering between the porous body and the water jacket forming die. Therefore, it is possible to reliably prevent casting defects due to cast cavities, formed by the air-bubbles left in the cylinder block material, and/or oxide films, included in the cylinder block material, from being caused near outer periphery of the metal matrix composite body.

[0030] A third aspect of the invention relates to a method for producing an open-deck cylinder block which is cast with a cylinder liner, used to form a wall of a cylinder bore, incorporated within the cylinder block, and in which a water jacket opens on a deck-face. According to this method, dies are clamped together with a cylindrical porous body closely fitted on the outer periphery of the cylinder liner at a deck-face portion of the cylinder block, with a bore pin closely fitted in the cylinder liner, and with a water jacket forming die closely fitted on the outer periphery of the porous body. The length of the porous body in the axial direction thereof is shorter than the length of the cylinder liner in the axial direction thereof. Then, the cylinder block is cast by die-casting with the cylinder liner and the porous body incorporated therein.

[0031] In the third aspect of the invention, the cylinder liner and the porous body may be heated with the porous body closely fitted on the outer periphery of the cylinder liner at the deck-face portion of the cylinder block; and the dies may be clamped together with the bore pin closely fitted in the cylinder liner, and with the water jacket forming die closely fitted on the outer periphery of the porous body. This preheating process prevents the situation in which the temperature of the molten metal is abruptly decreased during the casting process and therefore the fluidity of the molten metal is reduced. Accordingly, the porous body is impregnated with the molten metal appropriately. [0032] The invention provides the open-deck cylinder block. In the deck-face portion on which the cylinder head is fitted, the metal matrix composite body formed of the MMC is closely fitted on the outer periphery of the cylinder liner. The outer periphery of the metal matrix composite body faces the water jacket. Thus, a layer made only from the material of the cylinder block body (for example, an aluminum alloy) is not formed in a portion of the deck-face portion, which is on the inner side of the water jacket. Accordingly, the deck-face portion is provided with a sufficient strength. In addition, because the entire inner periphery of the metal matrix composite body is kept in close contact with the outer periphery of the cylinder liner, such close contact between the metal matrix composite body and the cylinder liner is stably maintained over long periods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The features, advantages thereof, and technical and industrial significance of this invention will be better understood by reading the following detailed description of example embodiments of the invention, when considered in connection with the accompanying drawings, in which:

FIG. 1 is a plane view of a cylinder block according to a first embodiment of the invention; FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1;

FIG. 3 is a perspective view for describing the process in which cylinder liners and preforms are fitted to each other;

FIG. 4 is a cross-sectional view that shows the state in which the cylinder liner and the preform are arranged in a die, and that is taken along the plane perpendicular to the direction in which cylinders are aligned;

FIG. 5 is an enlarged cross-sectional view showing the preform and the portion near the preform when the cylinder liner and the preform are arranged in the die according to a second embodiment of the invention;

FIG. 6 is an enlarged cross-sectional view showing the preform and the portion near the preform when the cylinder liner and the preform are arranged in the die according to a third embodiment of the invention; and

FIG. 7 is an enlarged cross-sectional view showing the preform and the portion near the preform when the cylinder liner and the preform are arranged in the die according to a fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS [0034] In the following description and the accompanying drawings, the present invention will be described with reference to example embodiments. [0035] Hereafter, embodiments of the invention will be described with reference to the accompanying drawings. The following description will be provided on the assumption that each embodiment of the invention is applied to a cylinder block having the Siamese structure, which is employed in an in-line four-cylinder diesel engine for an automobile. [0036] A first embodiment of the invention will be described below. First, the structure of a cylinder block 1 will be schematically described. FIG. 1 is a plane view showing the cylinder block 1 of an in-line four-cylinder diesel engine according to the first embodiment of the invention (the view showing the end face of the upper portion of the cylinder block 1). Cylinder bores 11 and a portion near the cylinder bores 11 are shown in FIG. 1. FIG. 1 shows the manner in which a deck-face Ia (the top face of the cylinder block 1), namely, the face on which a cylinder head is fitted, a cylinder alignment, and a water jacket (a coolant passage) 12 are arranged. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1.

[0037] In the following description, a cylinder at the far left in FIG. 1 is referred to as a first cylinder #1, a second left cylinder in FIG. 1 is referred to as a second cylinder #2, a second right cylinder in FIG. 1 is referred to as a third cylinder #3, and a cylinder at the far right in FIG. 1 is referred to as a fourth cylinder #4. Also, the upper side in FIG. 1 is referred to as the intake side, and the lower side in FIG. 1 is referred to as the exhaust side. The number of cylinders and the configurations of an intake system and an exhaust system are not limited to those shown in FIG. 1.

[0038] Most part of the cylinder block 1 according to the first embodiment of the invention is made from an aluminum alloy. As shown in FIG. 1, the cylinder block 1 includes a Siamese cylinder barrel unit 2 having four cylinder barrels 21 that are arranged in line. The Siamese cylinder barrel unit 2 will be described later in detail.

[0039] The cylinder block 1 is an open-deck cylinder block. Namely, the water jacket 12 is open on the deck-face Ia of the cylinder block 1 on which the cylinder head is fitted.

[0040] The water jacket 12 is formed between the outer wall of the cylinder block 1 and the Siamese cylinder barrel unit 2 so as to surround substantially the entire periphery of the Siamese cylinder barrel unit 2. Accordingly, the water jacket 12 extends along the cylindrical faces that are the outer peripherys of the cylinder barrels 21, as shown in FIG.

1.

[0041] A coolant inlet passage 12a, through which a coolant supplied from a water pump (not shown) is introduced into the water jacket 12, is formed in one end portion

(the left end portion in FIG. 1) of the cylinder block 1, namely, in the portion near the first cylinder #1. The coolant inlet passage 12a extends in the direction in which the cylinders are aligned.

[0042] The coolant, introduced through the coolant inlet passage 12a, flows through the water jacket 12 formed within the cylinder block 1 substantially horizontally in the direction in which the cylinder barrels 21 are aligned, thereby cooling the cylinder block 1. More specifically, the flow of the coolant introduced through the coolant inlet passage 12a diverges in two directions, and one of the flows is directed toward the intake side that is the upper side of the Siamese cylinder barrel unit 2 in FIG. 1 and the other flow is directed toward the exhaust side that is the lower side of the Siamese cylinder barrel unit 2 in FIG. 1. Each flow is directed from the first cylinder #1 toward the fourth cylinder #4 substantially horizontally (the direction indicated by the arrows in FIG. 1). In this manner, the cylinder block 1 is cooled. The coolant that has been used to cool the cylinder block 1 is then introduced into a water jacket formed within the cylinder head to cool the cylinder head.

[0043] A plurality of head bolt holes 13 is formed in the cylinder block 1. Head bolts are inserted into the head bolt holes 13 to fit a cylinder head gasket and the cylinder head to each other. [0044] Next, the Siamese cylinder barrel unit 2 will be described. As described above, the Siamese cylinder barrel unit 2 includes the four cylinder barrels 21. Because the cylinder barrels 21 have the same structure, only one of these cylinder barrels 21 will be described below.

[0045] The cylinder barrel 21 includes a cylinder liner 3, and a short cylindrical body 4 having the metal matrix composite structure (hereinafter, referred to as a "MMC ring

4"). The MMC ring 4 is arranged on the outer side of the cylinder liner 3 so as to be along the outer periphery of the cylinder liner 3. The cylinder barrel 21 will be described below in detail.

[0046] The cylinder liner 3 is a cylindrical body made from cast-iron. The cylinder liner 3 is a member that forms the wall of the cylinder bore 11, along which a piston slides. The cylinder liner 3 provides the face having sufficient mechanical strength, abrasion resistance, thermal resistance, etc.

[0047] The MMC ring 4 is a metal matrix composite that is formed by impregnating a porous preform 41, which is formed into a substantially cylindrical shape in advance, with a molten aluminum alloy (material of the cylinder block) (see FIG. 3) in the die-casting process.

[0048] The MMC ring 4 is formed such that the inner diameter of the MMC ring 4 is substantially equal to the outer diameter of the cylinder liner 3, whereby the inner periphery of the MMC ring 4 is kept in close contact with the outer periphery of the cylinder liner 3. At the same time, the outer periphery of the MMC ring 4 faces the water jacket 12. A fitting face 42 of each MMC ring 4, on which the MMC ring 4 of the adjacent cylinder is fitted, is flat. These fitting faces 42 of the adjacent MMC rings 4 are kept in close contact with each other. Accordingly, an outer periphery 43 of the MMC ring 4, which does not include the fitting face 42, faces the water jacket 12. [0049] The MMC ring 4 is considerably shorter in length in the axial direction of the cylinder (substantially vertical direction) than the cylinder liner 3 (for example, the length of the MMC ring 4 is approximately one tenths (1/10) of the length of the cylinder liner 3). The cylinder liner 3 and the MMC ring 4 are integrally incorporated within the cylinder block 1 in the casting process such that an upper-end face 4a of the MMC ring 4 and an upper-end face 3a of the cylinder liner 3 are substantially coplanar with the deck-face Ia of the cylinder block 1.

[0050] The lower portion of the cylinder liner 3 extends to a position near a skirt portion Ib (a portion that forms the upper-side portion of a crank chamber) of the cylinder block 1. An aluminum alloy portion (a portion made from the material of the cylinder block 1) is present between the water jacket 12 and the outer periphery of a portion of the cylinder liner 3, the portion being below the MMC ring 4.

[0051] The process for integrally incorporating the cylinder liner 3 and the MMC ring 4 within the cylinder block 1 in the casting process will be described later. [0052] As described above, the deck-face portion of the cylinder barrel 21 has the two-layer structure including the cylinder liner 3 and the MMC ring 4 which is arranged on the outer side of the cylinder liner 3 so as to be along the outer periphery of the cylinder liner 3. Accordingly, a layer formed only from the aluminum alloy that is the material of the cylinder block 1 (the aluminum alloy layer which has not become the MMC) is not formed at the deck-face portion. Namely, only the two-layer structure including the cylinder liner 3 and the MMC ring 4 is present between the cylinder bore 11 and the water jacket 12, at the deck-face portion.

[0053] Next, the casting process for producing the cylinder block 1 having the above-mentioned structure will be described. [0054] In the preliminary process performed before the casting process, the cylinder liner 3 and the preform (porous body) 41 are fitted to each other. Then, the die-casting process is performed with a cylinder barrel assembly, formed by fitting the cylinder liner 3 and the preform 41 to each other, arranged in a die 5 (see FIG. 4).

[0055] First, the process for fitting the cylinder liner 3 and the preform 41 to each other will be described. Because the cylinder block 1 according to the first embodiment of the invention has four cylinders, the four cylinder liners 3 and the four preforms 41 are used, as shown in FIG. 3.

[0056] Each cylinder liner 3 is the cylindrical body made from cast-iron, as described above. The cylinder liners 3 have the same structure.

[0057] The preforms 41 include outer preforms 41 A corresponding to the first cylinder #1 and the fourth cylinder #4, and inner preforms 41B corresponding to the second cylinder #2 and the third cylinder #3.

[0058] Each outer preform 41 A has one fitting face 42 on which the adjacent inner preform 41B is fitted. Each inner preform 41B has two fitting faces 42 on which the adjacent outer preform 41 A and the adjacent inner preform 4 IB are fitted, respectively.

[0059] These preforms 41 A and 4 IB are made of ceramic fibers. For example, the ceramic fibers contain, for example, alumina fibers and carbon fibers. The alumina fibers contain 97% alumina and 3% silica, and the carbon fibers contain 99.7% carbon. Each of the alumina fiber and the carbon fiber has an average length of 70 μm to 130 μm, and an average diameter of 3 μm to 6 μm. The percentage of fibers in the preforms 41 A and 41B is 12% to 21%. More specifically, the percentage of alumina fibers in the preforms 41 A and 41B is 8% to 16%, and the percentage of carbon fibers in the preforms

41 A and 41B is 4% to 5%. The percentages of alumina fibers and carbon fibers in the preforms 41A and 41B are adjusted such that percentage of fibers is 12% to 21 %. The length and the diameter of each of the alumina fiber and the carbon fiber are set to the above-mentioned values, because the amount of clearance between the adjacent fibers should be maintained at 20 μm to 80 μm to efficiently impregnate the preforms 41 A and

41B with the molten aluminum alloy. The preforms 41 A and 4 IB are formed by bonding the alumina fibers and the carbon fibers together using a ceramic binder.

[0060] The material of the preforms 41 A and 41B is not limited to ceramic fibers. The preforms 41 A and 4 IB may be made of any suitable fiber material or a porous metal material. Namely, any materials may be used as long as the preforms 41 A and 4 IB trap air-bubbles and aluminum-alloy oxide films contained in the molten aluminum alloy in the die-casting process described later. '

[0061] The cylinder liners 3 are fitted into the preform 41 A and 41 B under pressure such that the upper-end faces 4a of the preforms 41 A and 4 IB and the upper-end faces 3a of the cylinder liners 3 are coplanar with each other. In this way, the outer periphery of the cylinder liner 3 and the entire inner periphery of the preform 41 are brought into close contact with each other.

[0062] Then, the cylinder barrel assembly formed by fitting the cylinder liner 3 and the preform 41 to each other is preheated. The cylinder barrel assembly is heated. in a heating furnace at, for example, approximately 400 ⁰C for a predetermined time. Such preheating process is performed to facilitate impregnation of the preform 41 with the molten aluminum alloy in the die-casting process, which will be performed after the preheating process. The temperature at which the preform 41 is preheated is not limited to approximately 400 ⁰C. For example, the temperature may be approximately 500 ⁰C.

Also, the preheating method is not limited to the above-described one. The electromagnetic induction method may be employed to preheat the preform 41.

[0063] The preforms 41 A and 41B to which the cylinder liners 3 are fitted are arranged in the die 5 with the fitting faces 42 thereof kept in close contact with each other.

FIG. 4 is a cross-sectional view that shows the state where the cylinder liner 3 and the preform 41 are arranged in the die 5, and that is taken along the plane perpendicular to the direction in which the cylinders are aligned.

[0064] As shown in FIG. 4, the die 5 includes a bore pin 51, a water jacket forming die 52, a side die 53, and a lower die 54.

[0065] The bore pin 51 is a cylindrical member having the outer diameter that is substantially equal to the inner diameter of the cylinder liner 3. When the dies are clamped together, the bore pin 51 is inserted into the cylinder liner 3. The water jacket forming die 52 has a pin hole 52a in which the bore pin 51 is inserted, and a water jacket forming portion 52b used to form the water jacket 12. When the dies are clamped together, a lower-end face 4b of the preform 41 faces a cavity 57 formed between the water jacket forming portion 52b and the cylinder liner 3. The side die 53 is used to form the outer wall of the cylinder block 1. A cavity 55 having a predetermined amount is formed between the side die 53 and the water jacket forming portion 52b, and a cavity 58 having a predetermined amount is formed between the side die 53 and the cylinder liner 3. The lower die 54 is used to form the skirt portion Ib of the cylinder block 1, and fixed at a position at which the lower die 54 contacts the tip-end face of the bore pin 51. A cavity 56 having a predetermined amount is formed between the lower die 54 and the side die 53. In this state, a lower-end face 3b of the cylinder liner 3 faces the cavity 56.

[0066] The die 5 is clamped with the cylinder liner 3 and the preform 41 arranged therein, and the molten aluminum alloy, which is the material of the cylinder block 1, is poured, under a predetermined pressure, through the cavity 56 formed between the lower die 54 and the side die 53.

[0067] The molten aluminum alloy flows through the cavity 56 formed between the lower die 54 and the side die 53, flows through the cavity 58 and then the cavity 57, and finally reaches the lower-end face 4b of the preform 41, whereby the preform 41 is impregnated with the molten aluminum alloy. Thus, the MMC is formed by the preform

41 and the aluminum alloy, and this MMC portion is used as the MMC ring 4.

[0068] The presence of the preform 41 prevents the air-bubbles and aluminum-alloy oxide films contained in the molten aluminum alloy from reaching the inner portion of the preform 41, because these air-bubbles and oxide films are trapped in the portion near the lower-end face 4b of the preform 41. Thus, the inner portion of the MMC ring 4 is free of casting defects due to the cast cavities and/or inclusion of oxide films.

[0069] Meanwhile, the molten aluminum alloy poured into the cavity 55 between the water jacket forming die 52 and the side die 53 forms the outer wall of the cylinder block 1. [0070] Thus, the water jacket 12 is formed between the aluminum-alloy portion formed by the molten aluminum alloy poured into the cavity 55, and the aluminum-alloy portion formed by the molten aluminum alloy poured into the cavity 57 and the MMC ring 4 (see FIG. 2).

[0071] As described above, the molten aluminum alloy is poured into the cavities 55, 56, 57 and 58, and the preform 41 becomes the MMC to form the MMC ring 4. In this state, the aluminum alloy is cooled and solidified. Then, the dies are removed, whereby the cylinder block 1 having the structure described above is obtained.

[0072] In the cylinder block 1 produced by the casting method, as described above, the deck-face portion of the cylinder barrel 21 has the two-layer structure including the cylinder liner 3 and the MMC ring 4 which is arranged on the outer side of the cylinder liner 3 so as to be along the outer periphery of the cylinder liner 3. A layer formed only from the aluminum alloy, which is the material of the cylinder block 1, (the layer of the aluminum alloy which has not become the MMC) is not formed at the deck-face portion. Namely, as shown in FIGs. 1 and 2, only the two-layer structure including the cylinder liner 3 and the MMC ring 4 is present between the cylinder bore 11 and the water jacket 12 at the deck-face portion. Therefore, according to the first embodiment of the invention, only the cylinder liner 3 and the MMC ring 4 are present in the portion on the inner side of the water jacket 12, in the deck-face Ia and the portion near the deck-face Ia that should be provided with the highest strength in the cylinder block 1. Accordingly, the layer formed only from the aluminum alloy (the material that has not become the MMC), which is the material of the cylinder block, is not formed in this portion. Therefore, casting defects due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy, are not caused in the deck-face Ia and the portion near the deck-face Ia in the cylinder block 1. As a result, this portion is provided with a sufficient strength. In addition, the entire inner periphery of the MMC ring 4 is kept in close contact with the outer periphery of the cylinder liner 3. Accordingly, it is possible to stably maintain such close contact between the MMC ring 4 and the cylinder liner 3 over long periods. [0073] Also, the preform 41 is formed into a substantially cylindrical shape having a short length. Namely, the preform 41 is formed such that the length thereof in the direction in which the molten aluminum alloy flows is relatively short. Therefore, the molten aluminum alloy easily reaches the deck-face Ia, and the amount of molten aluminum alloy that reaches the deck-face Ia does not become insufficient. [0074] The MMC (metal matrix composite) that forms the MMC ring 4 have the physical properties such as a thermal expansion rate of 17 x 10^~6 to 18 x 1(X⁶ / ⁰C, a Young's modulus of 200 Mpa to 250 Mpa, and a Vickers hardness of 135 to 150. A common aluminum alloy for die-casting has a thermal expansion rate of approximately 20 x 10^"6/ ⁰C, a Young modulus of 150 Mpa to 250 Mpa, and a Vickers hardness of 98 to 105. Accordingly, provision of the MMC ring 4 produces excellent effects. For example, deformation of the wall of the cylinder bore 11 is suppressed (the circularity of the wall of the cylinder bore 11 is maintained) due to a restricted thermal expansion rate; the strength of the wall of the cylinder bore 11 is enhanced due to an increased Young's modulus; and high sealing properties is maintained because indentation at the portion at which the head gasket contacts the cylinder block 1 is suppressed due to an increased Vickers hardness.

[0075] Next, a second embodiment of the invention will be described. The second embodiment of the invention differs from the first embodiment of the invention only in the shape of the preform 41. The other structures and the casting method are the same as those according to the first embodiment of the invention. Accordingly, mainly the shape of the preform 41 will be described below.

[0076] FIG. 5 is an enlarged cross-sectional view showing the preform 41 and the portion near the preform 41 when the cylinder liner 3 and the preform 41 are arranged in the die 5 according to the second embodiment of the invention.

[0077] As shown in FIG. 5, the lower-end face 4b (the face that faces the cavity 57) of the preform 41 according to the second embodiment of the invention is sloped upward

(toward the deck-face: left side in FIG. 5) toward the inner peripheral side. In other words, the lower-end face 4b of the preform 41 is sloped such that one end thereof close to the cylinder liner 3 is located downstream of the other end thereof close to the water jacket 12 in the direction in which the molten aluminum alloy flows. The other portions of the preform 41 according to the second embodiment of the invention have the same shapes as those of the preform 41 according to the first embodiment of the invention.

[0078] When the molten aluminum alloy is poured into the die 5 with the thus shaped preform 41 arranged in the die 5 and then flows through the cavity 57 toward the inside portion of the preform 41, the air-bubbles and/or aluminum-alloy oxide films contained in the molten aluminum alloy are carried toward the inner periphery of the preform 41 and accumulated near the inner periphery of the preform 41 (see the arrows indicated by the dashed lines in FIG. 5). Accordingly, after the aluminum alloy is cooled and solidified, the outer peripheral-side portion (the water jacket 12-side portion) of the aluminum alloy portion that faces the lower-end face 4b of the preform 41 is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy. [0079] The stress of the cylinder pressure in the power stroke of the engine is largely applied to the outer peripheral-side portion of the cylinder barrel 21. However, the outer peripheral-side portion to which such large stress is applied is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy. Accordingly, this portion is provided with a sufficient strength. As a result, it is possible to improve the reliability of the cylinder block 1.

[0080] Next, a third embodiment of the invention will be described. The third embodiment of the invention differs from the first embodiment of the invention only in the shape of the preform 41. The other structures and the casting method are the same as those according to the first embodiment of the invention. Accordingly, mainly the shape of the preform 41 will be described below.

[0081] FIG. 6 is an enlarged cross-sectional view showing the preform 41 and the portion near the preform 41 when the cylinder liner 3 and the preform 41 are arranged in the die 5 according to the third embodiment of the invention. [0082] As shown in FIG. 6, the lower-end face 4b (the face that faces the cavity 57) of the preform 41 according to the third embodiment of the invention has a recess 4c at its center. The recess 4c is formed into a circular shape of which the center matches the axis of the preform 41. In other words, the lower-end face 4b of the preform 41 has the recess 4c at its center that is between one end thereof close to the cylinder liner 3 and the other end thereof close to the water jacket 12. The other portions according to the third embodiment of the invention have the same shapes as those according to the first embodiment of the invention.

[0083] When the molten aluminum alloy is poured into the die 5 with the thus shaped preform 41 arranged in the die 5 and then flows through the cavity 57 toward the inside portion of the preform 41, the air-bubbles and/or aluminum-alloy oxide films contained in the molten aluminum alloy are carried toward the recess 4c formed in the lower-end face 4b of the preform 41 and accumulated in the recess 4c (see the arrows indicated by the dashed lines in FIG. 6). Accordingly, after the aluminum alloy is cooled and solidified, the outer peripheral-side portion (the water jacket 12-side portion) of the aluminum alloy portion that faces the lower-end face 4b of the preform 41 is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy.

[0084] As described above, a stress of the cylinder pressure in the power stroke of the engine is largely applied to the outer peripheral-side portion of the cylinder barrel 21. However, the outer peripheral-side portion to which such large stress is applied is free of casting defects caused due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy. Accordingly, this portion is provided with a sufficient strength. As a result, it is possible to improve the reliability of the cylinder block 1.

[0085] A fourth embodiment of the invention will be described below. The fourth embodiment of the invention also differs from the first embodiment of the invention only in the shape of the preform 41. The other structures and the casting method according to the fourth embodiment of the invention are the same as those according to the first embodiment of the invention. Accordingly, mainly the shape of the preform 41 will be described below.

[0086] FIG. 7 is an enlarged cross-sectional view showing the preform 41 and the portion near the preform 41 when the cylinder liner 3 and the preform 41 are arranged in the die 5 according to the fourth embodiment of the invention. In FIG. 7, the cross-section of the preform 41 before the dies are clamped is indicated by the dashed lines.

[0087] As shown in FIG. 7, the preform 41 according to the fourth embodiment of the invention is formed such that the inner diameter of the portion proximal to the deck-face (the left side in FIG. 7) is smaller than the inner diameter of the portion distal to the deck-face (the right side in FIG. 7). The inner diameter of the portion distal to the deck-face is substantially equal to the outer diameter of the cylinder liner 3. Meanwhile, the inner diameter of the portion proximal to the deck-face is slightly smaller than the outer diameter of the cylinder liner 3. [0088] Setting the inner diameters of the preform 41 in this manner facilitates the process of fitting the cylinder liner 3 into the preform 41 under pressure. In addition, after the cylinder liner 3 is fitted into the preform 41, no clearance is left between the preform 41 and the cylinder liner 3. Accordingly, a layer made only from the material of the cylinder block 1 (aluminum alloy) is not formed between the preform 41 and the cylinder liner 3. Therefore, it is possible to reliably prevent casting defects due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy from being caused between the preform 41 and the cylinder liner 3.

[0089] Another feature of the preform 41 according to the fourth embodiment is its outer shape. The outer diameter of the portion proximal to the deck-face (the portion on the left side in FIG. 7) is smaller than the outer diameter of the portion distal to the deck-face (the portion on the right side in FIG. 7). In addition, the outer diameter of the portion on the deck-face side is substantially equal to the inner diameter of the water jacket forming portion 52b of the water jacket forming die 52. Meanwhile, the outer diameter of the portion distal to the deck-face is slightly larger than the inner diameter of the water jacket forming portion 52b of the water jacket forming die 52;

[0090] Setting the outer diameters of the preform 41 in this way facilitates the process of fitting the water jacket forming die 52 from the deck-face side of the preform 41. In addition, when the dies are clamped together, no clearance is left between the outer periphery of the preform 41 and the water jacket forming die 52. Accordingly, it is possible to prevent the cylinder block material (aluminum alloy) in the form of molten metal from entering between the preform 41 and the water jacket forming die 52. Therefore, it is possible to reliably prevent casting defects due to cast cavities, formed by the air-bubbles left in the molten aluminum alloy, and/or oxide films, included in the aluminum alloy, from being caused near outer periphery of the MMC ring 4.

[0091] The structure according to the fourth embodiment of the invention may be combined with the structure according to the second embodiment of the invention or the structure according to the third embodiment of the invention. [0092] Each embodiment of the invention described above is applied to the cylinder block 1 having the Siamese structure, which is employed in an in-line four-cylinder diesel engine for an automobile. Alternatively, the invention may be applied to other types of diesel engines and gasoline engines. In addition, the invention may be applied to cylinder blocks that do not have the Siamese structure. Further, the invention may be applied not only to engines for automobiles but also engines for other uses. The invention may be applied to engines having any number of cylinders and any engine configurations (in-line engines, V-type engines, horizontal opposed engines).

Claims

CLAIMS:

1. An open-deck cylinder block which is cast with a cylinder liner, used to form a wall of a cylinder bore, incorporated within the cylinder block, and in which a water jacket opens on a deck-face, characterized in that a metal matrix composite body that is formed by impregnating a cylindrical porous body with a cylinder block material is fitted on an outer periphery of the cylinder liner at a deck-face portion of the cylinder block, wherein a length of the porous body in an axial direction of the porous body is shorter than a length of the cylinder liner in an axial direction of the cylinder liner, an outer periphery of the metal matrix composite body faces the water jacket, and an entire inner periphery of the metal matrix composite body is kept in close contact with the outer periphery of the cylinder liner, and an inner periphery of the cylinder liner faces the cylinder bore.

2. The open-deck cylinder block according to claim 1, characterized in that a casting process is performed with the porous body fitted on the outer periphery of the cylinder liner at the deck-face portion of the cylinder block, whereby only the cylinder liner and the metal matrix composite body are present between the cylinder bore and the water jacket, at the deck-face portion of the cylinder block.

3. An open-deck cylinder block which is cast with a cylinder liner, used to form a wall of a cylinder bore, incorporated within the cylinder block, and in which a water jacket opens on a deck-face, characterized in that a casting process is performed with a cylindrical porous body fitted on an outer periphery of the cylinder liner at a deck-face portion of the cylinder block, a length of the porous body in an axial direction of the porous body being shorter than a length of the cylinder liner in an axial direction of the cylinder liner, whereby only the cylinder liner and a metal matrix composite body formed by impregnating the porous body with a cylinder block material are present between the cylinder bore and the water jacket, at the deck-face portion of the cylinder block.

4. The open-deck cylinder block according to any one of claims 1 through 3, characterized in that the porous body is fitted, under pressure, on the outer periphery of the cylinder liner, and then the porous body is impregnated with the cylinder block material, whereby the metal matrix composite body is formed.

5. The open-deck cylinder block according to claim 4, characterized in that the porous body before being fitted on the outer periphery of the cylinder liner is shaped such that an inner diameter of a portion of the porous body, which is proximal to the deck-face of the cylinder block is smaller than an inner diameter of a portion of the porous body, which is distal to the deck-face of the cylinder block.

6. The open-deck cylinder block according to claim 4, characterized in that the porous body before dies are clamped together is shaped such that an outer diameter of a portion of the porous body, which is proximal to the deck-face of the cylinder block is smaller than an outer diameter of a portion of the porous body, which is distal to the deck-face of the cylinder block.

7. The open-deck cylinder block according to any one of claims 1 through 4, characterized in that the metal matrix composite body is formed by impregnating the porous body with the cylinder block material that flows, in a form of molten metal, in the axial direction of the cylinder liner, and a face of the porous body, through which the cylinder block material in the form of molten metal flows into the porous body, is sloped such that a cylinder liner-side end of the face is positioned downstream of a water jacket-side end of the face in a direction in which the cylinder block material in the form of molten metal flows.

8. The open-deck cylinder block according to any one of claims 1 through 4, characterized in that the metal matrix composite body is formed by impregnating the porous body with the cylinder block material that flows, in a form of molten metal, in the axial direction of the cylinder liner, and a face of the porous body, through which the cylinder block material in the form of molten metal flows into the porous body, has a recess at a center between a cylinder liner-side end of the face and a water jacket-side end of the face.

9. A method for producing an open-deck cylinder block which is cast with a cylinder liner, used to form a wall of a cylinder bore, incorporated within the cylinder block (1), and in which a water jacket opens on a deck-face, characterized by comprising: clamping dies together with a cylindrical porous body closely fitted on an outer periphery of the cylinder liner at a deck-face portion of the cylinder block, with a bore pin closely fitted in the cylinder liner, and with a water jacket forming die closely fitted on an outer periphery of the porous body, wherein a length of the porous body in an axial direction of the porous body is shorter than a length of the cylinder liner in an axial direction of the cylinder liner; and casting the cylinder block by die-casting with the cylinder liner and the porous body incorporated within the cylinder block.

10. The method for producing an open-deck cylinder block according to claim 9, characterized by further comprising: heating the cylinder liner and the porous body with the porous body closely fitted on the outer periphery of the cylinder liner at the deck-face portion of the cylinder block; and clamping the dies together with the bore pin closely fitted in the cylinder liner, and with the water jacket forming die closely fitted on the outer periphery of the porous body.

11. An open-deck cylinder block, comprising: a cylinder liner that forms a wall of a cylinder bore formed within the cylinder block and that is incorporated within the cylinder block in a casting process; a water jacket which is formed within the cylinder block, which opens on a deck-face of the cylinder block, and through which a coolant that cools the cylinder block flows; and a metal matrix composite body that is formed by impregnating a cylindrical porous body with a cylinder block material, wherein a length of the porous body in an axial direction of the porous body is shorter than a length of the cylinder liner in an axial direction of the cylinder liner, an outer periphery of the metal matrix composite body faces the water jacket, an entire inner periphery of the metal matrix composite body is closely fitted on an outer periphery of the cylinder liner, and an inner periphery of the cylinder liner faces the cylinder bore.

12. The open-deck cylinder block according to claim 11, wherein a casting process is performed with the porous body fitted on the outer periphery of the cylinder liner at a deck-face portion of the cylinder block, whereby only the cylinder liner and the metal matrix composite body are present between the cylinder bore and the water jacket, at the deck-face portion of the cylinder block.

13. An open-deck cylinder block, comprising: a cylinder liner that forms a wall of a cylinder bore formed within the cylinder block and that is incorporated within the cylinder block in a casting process; a water jacket which is formed within the cylinder block, which opens on a deck-face of the cylinder block, and through which a coolant that cools the cylinder block flows; and a metal matrix composite body that is formed by impregnating a cylindrical porous body with a cylinder block material, wherein a length of the porous body in an axial direction of the porous body is shorter than a length of the cylinder liner in an axial direction of the cylinder liner, and a casting process is performed with the porous body fitted on the outer periphery of the cylinder liner at a deck-face portion of the cylinder block, whereby only the cylinder liner and the metal matrix composite body are present between the cylinder bore and the water jacket, at the deck-face portion of the cylinder block.

14. The open-deck cylinder block according to any one of claims 11 through 13, wherein the porous body is fitted, under pressure, on the outer periphery of the cylinder liner, and then the porous body is impregnated with the cylinder block material, whereby the metal matrix composite body is formed.

15. The open-deck cylinder block according to claim 14, wherein the porous body before being fitted on the outer periphery of the cylinder liner is shaped such that an inner diameter of a portion of the porous body, which is proximal to the deck-face of the cylinder block is smaller than an inner diameter of a portion of the porous body, which is distal to the deck-face of the cylinder block.

16. The open-deck cylinder block according to claim 14, wherein the porous body before dies are clamped together is shaped such that an outer diameter of a portion of the porous body, which is proximal to the deck-face of the cylinder block is smaller than an outer diameter of a portion of the porous body, which is distal to the deck-face of the cylinder block.

17. The open-deck cylinder block according to any one of claims 11 through 14, wherein the metal matrix composite body is formed by impregnating the porous body with the cylinder block material that flows, in a form of molten metal, in the axial direction of the cylinder liner, and a face of the porous body, through which the cylinder block material in the form of molten metal flows into the porous body, is sloped such that a cylinder liner-side end of the face is positioned downstream of a water jacket-side end of the face in a direction in which the cylinder block material in the form of molten metal flows.

18. The open-deck cylinder block according to any one of claims 11 through 14, wherein the metal matrix composite body is formed by impregnating the porous body with the cylinder block material that flows, in a form of molten metal, in the axial direction of the cylinder liner, and a face of the porous body, through which the cylinder block material in the form of molten metal flows into the porous body, has a recess at a center between a cylinder liner-side end of the face and a water jacket-side end of the face.

19. A method for producing an open-deck cylinder block in which a water jacket opens on a deck-face of the cylinder block, comprising: closely fitting a cylindrical porous body on an outer periphery of the cylinder liner at a deck-face portion of the cylinder block, wherein a length of the porous body in an axial direction of the porous body is shorter than a length of the cylinder liner in an axial direction of the cylinder liner, clamping dies together with a bore pin closely fitted in the cylinder liner, and with a water jacket forming die closely fitted on an outer periphery of the porous body; and casting the cylinder block by die-casting with the cylinder liner and the porous body incorporated within the cylinder block.

20. The method for producing an open-deck cylinder block according to claim 19, further comprising: heating the cylinder liner and the porous body with the porous body closely fitted on the outer periphery of the cylinder liner at the deck-face portion of the cylinder block; and clamping the dies together with the bore pin closely fitted in the cylinder liner, and with the water jacket forming die closely fitted on the outer periphery of the porous body.