WO2008059329A1

WO2008059329A1 - Cylinder block and method for producing cylinder block

Info

Publication number: WO2008059329A1
Application number: PCT/IB2007/003278
Authority: WO
Inventors: Toshihiro Takami; Kazuya Yoshijima
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-11-17
Filing date: 2007-10-30
Publication date: 2008-05-22
Also published as: JP4329809B2; JP2008128053A

Abstract

In an open-deck cylinder block (1) which is cast with a cylinder liner (3) incorporated therein, a MMC sleeve (4) that is made from a metal matrix composite is closely fitted on the outer periphery of the cylinder liner (3) and the outer periphery of the MMC sleeve (4) faces a water jacket (12), at a deck-face portion of the cylinder block (1). Thus, a layer made only from an aluminum alloy is not present in the deck-face portion, whereby the strength of the deck-face portion is enhanced. Also, the strength of the entire cylinder bore portion is enhanced by fitting the MMC sleeve (4) on the entire outer periphery of the cylinder liner (3). Thus, it is possible to provide an open-deck cylinder block having an enhanced strength at its upper-end portion of the cylinder block, and a method for producing such cylinder block.

Description

CYLINDER BLOCK AND METHOD FOR PRODUCING CYLINDER BLOCK

BACKGROUND OF THE 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 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 in production of the cylinder blocks in order 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. 2000-202613 (JP-A-2000-202613) 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-2000-202613, a reinforcing fiber preform is fitted inside a water-jacket forming core, a clearance is created inside the reinforcing fiber preform, and a cylinder-bore forming bore pin is arranged in the clearance. In this state, a process for casting a cylinder block is performed. In other words, the clearance between the reinforcing fiber preform and the cylinder-bore forming bore pin is used as a runner through which the molten metal flows. While the molten metal flows through the clearance, the reinforcing fiber preform becomes a MMC and is incorporated within cylinder block.

[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 clearance 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] Especially, in the cylinder block described in JP-A-63- 19050, the reinforcing preform is fitted on only a portion of the cylinder liner in the axial direction of the cylinder liner. Accordingly, the degree of closeness at which a cylinder block body (a portion made from an aluminum alloy) and the cylinder liner are fitted to each other varies from portion to portion of the cylinder liner in its axial direction. Therefore, the degree of closeness at which the cylinder liner is fitted to the cylinder block body would be significantly reduced by metal fatigue. Such metal fatigue is caused by alternately repeating heat expansion and heat shrinkage of the cylinder liner in its axial direction.

[0014] In the cylinder block described in JP-A-2000-202613, the clearance between the reinforcing fiber preform and cylinder-bore forming bore pin is used as the runner through which the molten metal flows, as described above, and the runner reaches the upper-end portion of the cylinder block. In the cylinder block described in JP-A-2000-202613, the reinforcing preform is incorporated within the portion (upper-end portion of the cylinder block) that should be provided with the highest strength. However, the material that forms the cylinder block flows, in the form of molten metal, along the inner periphery of the reinforcing preform. Therefore, 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 as well, the strength of this defective portion may be insufficient.

SUMMARY OF THE INVENTION

[0015] The invention is made in the light of the above-described circumstances. The invention provides an open-deck cylinder block in which a cylinder-head side portion (an upper-end portion of the cylinder block) is provided with a high strength while a cylinder liner is reliably kept in close contact with another member. The invention also provides a method for producing such cylinder block.

[0016] 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 present in a portion of the deck-face portion, which is on the inner side of the water jacket. Also, the MMC portion is fitted on the entire outer periphery of the cylinder liner. This makes it possible to provide high strength to the entire cylinder bore portion, and to maintain high circularity of the cylinder bore.

[0017] A first aspect of the invention relates to 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. In the cylinder block, a metal matrix composite body formed by impregnating a cylindrical porous body with a cylinder block material is fitted on the entire outer periphery of the cylinder liner. At a deck-face portion of the cylinder block (a portion of the cylinder block, on which a cylinder head is fitted), the inner periphery of the cylinder liner faces the cylinder bore, and the outer periphery of the metal matrix composite body faces the water jacket. The outer periphery of the cylinder liner and the inner periphery of the metal matrix composite body are kept in close contact with each other

[0018] A second aspect of the invention relates to 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. In the cylinder block, a casting process is performed with a cylindrical porous body fitted on the entire outer periphery of the cylinder liner. 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 a deck-face portion of the cylinder block.

[0019] 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 metal matrix composite body is fitted on the entire outer periphery of the cylinder liner. Accordingly, the degree of closeness at which the metal matrix composite body and the cylinder liner are fitted to each other is uniform in the entire region in the axial direction of the cylinder liner. Therefore, the metal matrix composite body and the cylinder liner are reliably kept in close contact with each other over long periods.

[0020] The shape of the porous body is classified into two types described below. In the first type, the cross-section that is perpendicular to the axis of the porous body is uniform in shape throughout the porous body in its axial direction. The substantial entirety of the inner peripheral side of the water jacket, which is formed on the outer peripheral side of the cylinder bore, faces the metal matrix composite body. In the second type, a portion of the porous body, which is other than the deck-face portion in the porous body, is formed as a small-diameter portion that has the outer diameter smaller than the outer diameter of the deck-face portion in the porous body. The cylinder block material is present on the outer periphery of the small-diameter portion. In the second type, a portion of the porous body, which is other than the deck-face portion in the porous body and a lower-end portion of the porous body, the lower-end portion being farthest from the deck-face in the porous body, may be formed as a small-diameter portion that has the outer diameter smaller than the outer diameter of each of the deck-face portion and the lower-end portion in the porous body. The cylinder block material is present on the outer periphery of the small-diameter portion. In the second type, portions of the porous body, which are other than the deck-face portion in the porous body and a center portion that is present between the deck-face portion and a lower-end portion of the porous body, the lower-end portion being farthest from the deck-face in the porous body, may be formed as small-diameter portions each of which has the outer diameter smaller than the outer diameter of each of the deck-face portion and the center portion in the porous body. The cylinder block material is present on the outer periphery of the small-diameter portion that is proximal to the deck-face.

[0021] The first type of porous body is formed easily, because the shape of the porous body is simple. Also, the metal matrix composite body formed by impregnating the porous body with the cylinder block material is sufficiently thick.

[0022] With the second type of porous body, the space formed on the outer periphery of the small-diameter portion of the porous body is used as a runner through which the cylinder block material in the form of molten metal flows. Therefore, the molten metal smoothly flows into each portion within the die, and each portion of the porous body is impregnated with the cylinder block material appropriately.

[0023] A method for producing the cylinder block having the above-described structure is within the scope of the invention. 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, a cylindrical porous body is closely fitted on the entire outer periphery of the cylinder liner that is used to form a wall of a cylinder bore. Dies are clamped together with a bore pin closely fitted in the cylinder liner and a water-jacket forming die closely fitted on the outer periphery of the porous body. Then, the cylinder liner and the porous body are incorporated within the cylinder block by die-casting.

[0024] In the third aspect of the invention, the cylinder liner and the porous body may be heated with the cylindrical porous body closely fitted on the entire outer t periphery of the cylinder liner. After heating the cylinder liner and the porous body, the dies may be clamped together with the bore pin closely fitted in the cylinder liner and the water-jacket forming die closely fitted on the outer periphery of the porous body. This preheating process prevents occurrence of 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.

[0025] 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 present 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, the metal matrix composite body is fitted on the entire outer periphery of the cylinder liner. Accordingly, the degree of closeness at which the metal matrix composite body and the cylinder liner are fitted to each other is uniform in the entire region in the axial direction of the cylinder liner. Therefore, the metal matrix composite body and the cylinder liner are reliably kept in close contact with each other over long periods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The features, advantages thereof, and technical and industrial significance of this invention will be better understood by reading the following detailed description of 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 each embodiment of the invention;

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

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

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 according to the first embodiment of the invention;

FIG. 5 is a cross-sectional view that shows the state in which the cylinder liner and the preform are arranged in the die, and that is taken along the plane perpendicular to the direction in which cylinders are aligned according to a second embodiment of the invention;

FIG. 6 is a cross-sectional view taken along the line II-II in FIG. 1 according to the second embodiment of the invention;

FIG. 7 is a cross-sectional view that shows the state in which the cylinder liner and the preform are arranged in the die, and that is taken along the plane perpendicular to the direction in which cylinders are aligned according to a third embodiment of the invention;

FIG. 8 is a cross-sectional view taken along the line II-II in FIG. 1 according to the third embodiment of the invention;

FIG. 9 is a cross-sectional view that shows the state in which the cylinder liner and the preform are arranged in the die, and that is taken along the plane perpendicular to the direction in which cylinders are aligned according to a fourth embodiment of the invention; and

FIG. 10 is a cross-sectional view taken along the line II-II in FIG. 1 according to the fourth embodiment of the invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] In the following description and the accompanying drawings, the present invention will be described with reference to example embodiments.

[0028] 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.

[0029] 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 each embodiment of the invention (a 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 IMI in FIG. 1.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 peripheries of the cylinder barrels 21, as shown in FIG. 1.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The cylinder barrel 21 includes a cylinder liner 3, and a cylindrical body 4 having the metal matrix composite structure (hereinafter, referred to as a "MMC sleeve 4"). The MMC sleeve 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 more detail.

[0039] 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 wall having sufficient mechanical strength, abrasion resistance, thermal resistance, etc.

[0040] The MMC sleeve (metal matrix composite body) 4 is made from a metal matrix composite (MMC) 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 described later in detail.

[0041] The MMC sleeve 4 is formed such that the inner diameter of the MMC sleeve 4 is substantially equal to the outer diameter of the cylinder liner 3, whereby the inner periphery of the MMC sleeve 4 is kept in close contact with the outer periphery of the cylinder liner 3. At the same time, most part of the outer periphery of the MMC sleeve 4 faces the water jacket 12. A fitting face 42 of each MMC sleeve 4, on which the MMC sleeve 4 of the adjacent cylinder is fitted, is flat. These fitting faces 42 of the adjacent MMC sleeves 4 are kept in close contact with each other. Accordingly, an outer periphery 43 of the MMC sleeve 4, which does not include the fitting face 42, faces the water jacket 12.

[0042] The MMC sleeve 4 and the cylinder liner 3 have substantially the same length in the axial direction of the cylinder (substantially vertical direction). The cylinder liner 3 and the MMC sleeve 4 are integrally incorporated within the cylinder block 1 in the casting process such that an upper-end face 4a of the MMC sleeve 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. Accordingly, a lower-end face 4b of the MMC sleeve 4 and a lower-end face 3b of the cylinder liner 3 are substantially coplanar with each other.

[0043] The lower portion of the MMC sleeve 4 and the lower portion of the cylinder liner 3 extend 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. The water jacket 12 is not present on the outer side of the lower portion of the MMC sleeve 4. At this portion (the region A in FIG. 2), the outer periphery of the MMC sleeve 4 is exposed to form a portion of the outer wall of the cylinder block 1. In other words, the MMC sleeve 4 serves also as a member that forms the outer wall of the cylinder block 1.

[0044] The process for integrally incorporating the cylinder liner 3 and the MMC sleeve 4 within the cylinder block 1 in the casting process will be described later in detail.

[0045] As described above, the cylinder barrel 21 has the two-layer structure including the cylinder liner 3 and the MMC sleeve 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 in the cylinder barrel 21. Namely, only the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 is present between the cylinder bore 11 and the water jacket 12.

[0046] Next, the casting process for producing the cylinder block 1 having the above-mentioned structure will be described.

[0047] 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).

[0048] 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.

[0049] Each cylinder liner 3 is the cylindrical body made from cast-iron, as described above. The cylinder liners 3 have the same structure.

[0050] 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.

[0051] 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.

[0052] 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 l6%, 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 41B are formed by bonding the alumina fibers and the carbon fibers together using a ceramic binder.

[0053] The material of the preforms 41 A and 4 IB 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. 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.

[0054] The cylinder liners 3 are fitted into the preforms 41 A and 4 IB under pressure such that the upper-end faces 4a of the preforms 41 A and 41B and the upper-end faces 3 a of the cylinder liners 3 are coplanar with each other, and the lower-end faces 4b of the preforms 41 A and 41B and the lower-end faces 3b of the cylinder liners 3 are coplanar with each other. In this way, the entire outer periphery of the cylinder liner 3 and the entire inner periphery of the preform 41 are brought into close contact with each other.

[0055] 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 °C 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 °C. Also, the preheating method is not limited to the above-described one. The electromagnetic induction method may be employed to preheat the preform 41.

[0056] The preforms 41 A and 41B in 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.

[0057] 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. [0058] 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. The side die 53 is used to form the outer wall of the cylinder block 1. A cavity 55, which is a predetermined amount of clearance, is formed between the side die 53 and the water-jacket forming portion 52b. A portion of the side die 53 contacts a portion (region A) of the outer periphery of the preform 41. The lower die 54 is used to form the skirt portion Ib of the cylinder block 1, and arranged so as to contact the tip-end face of the bore pin 51. A cavity 56, which is a predetermined amount of clearance, is formed between the lower die 54 and the side die 53. In this state, the lower-end face 3b of the cylinder liner 3 and the lower end face 4b of the preform 41 face the cavity 56.

[0059] 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.

[0060] The molten aluminum alloy flows through the cavity 56 formed between the lower die 54 and the side die 53, and reaches the lower-end face 4b of the preform 41. Then, the preform 41 is impregnated with the molten aluminum alloy. Thus, the MMC portion is formed by the preform 41 and the aluminum alloy, and this MMC portion is used as the MMC sleeve 4.

[0061] 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, a portion downstream (downstream in the direction in which the molten aluminum alloy flows) of the lower-end face 4b of the preform 41 is free of casting defects due to cast cavities and/or inclusion of oxide films.

[0062] The preform 41 is impregnated with the molten aluminum alloy, from which the air-bubbles and the oxide films have been removed in the above-described manner, to form the MMC sleeve 4. Then, the molten aluminum alloy is poured into the cavity 55 formed between the water-jacket forming die 52 and the side die 53 to form the outer wall of the cylinder block 1. As described above, the air-bubbles and aluminum-alloy oxide films contained in the molten aluminum alloy are trapped in the portion near the lower-end face 4b of the preform 41. Accordingly, the outer wall of the cylinder block 1 is also free of casting defects due to cast cavities and/or inclusion of oxide films. In this manner, the water jacket 12 is formed between the aluminum-alloy portion formed by the molten aluminum alloy poured into the cavity 55 and the MMC sleeve 4 (see FIG. 2).

[0063] As described above, the molten aluminum alloy is poured into the cavities 55 and 56, and the preform 41 becomes the MMC to form the MMC sleeve 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.

[0064] In the cylinder block 1 produced by the above-described casting method, the cylinder barrel 21 has the two-layer structure including the cylinder liner 3 and the MMC sleeve 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, as described above. A layer formed only from the aluminum alloy, which is the material of the cylinder block 1 , (the aluminum alloy layer which has not become the MMC) is not present in the cylinder barrel 21. Namely, as shown in FIGs. 1 and 2, only the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 is present between the cylinder bore 11 and the water jacket 12. Therefore, according to the first embodiment of the invention, only the cylinder liner 3 and the MMC sleeve 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, a layer formed only from the aluminum alloy (the material that has not become the MMC), which is the material of the cylinder block 1, is not present 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 deck¹face Ia in the cylinder block 1. As a result, this portion is provided with a sufficient strength. In addition, because the MMC sleeve 4 is formed on the entire outer periphery of the cylinder liner 3, the degree of closeness at which the MMC sleeve 4 and the cylinder liner are fitted to each other is uniform in the entire region in the axial direction of the cylinder liner 3. In addition, the MMC sleeve 4 and the cylinder liner 3 are reliably kept in close contact with each other over long periods.

[0065] The MMC (metal matrix composite) that forms the MMC sleeve 4 have the physical properties such as a thermal expansion rate of 17 x 10^~6 to 18 x 10^"6 / 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 sleeve 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.

[0066] 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. Accordingly, the shape of the MMC sleeve 4 in the second embodiment of the invention differs from that in the first embodiment of the invention. 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 and the shape of the MMC sleeve 4 that is formed by the preform 41 will be described below.

[0067] FIG. 5 is a cross-sectional view that shows the state in which 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 cylinders are aligned according to the second embodiment of the invention. [0068] As shown in FIG. 5, the preform 41 according to the second embodiment of the invention is formed such that the outer diameter of the upper-end portion (the left-side portion in FIG. 5: the deck-face portion) is different from the outer diameter of the other portion. As shown in FIG. 5, in the casting process, the cylinder block 1 is placed into a sideways position (i.e. the cylinder block 1 is placed such that the deck-face Ia faces the left side of FIG. 1. However, in the following description of the preform 41, the side on which the deck-face Ia is present will be referred to as the upper side and the side on which the crank case is present will be referred to as the lower side.

[0069] In the first embodiment of the invention, the outer diameter of the preform 41 is substantially equal to the inner diameter of the water-jacket forming portion 52b of the water-jacket forming die 52. Similarly, in the second embodiment of the invention, the outer diameter of the preform 41 at the upper-end portion (the deck-face portion) is substantially equal to the inner diameter of the water-jacket forming portion 52b of the water-jacket forming die 52.

[0070] In contrast, in the preform 41, the portion other than the upper-end portion is smaller in the outer diameter than the upper-end portion. The portion other than the upper-end portion is referred to as a small-diameter portion 44 of the preform 41. In other words, the preform 41 has a large-diameter portion 45 formed in the deck-face portion and the small-diameter portion 44 that is a portion of the preform 41 other than the large-diameter portion 45.

[0071] As shown in FIG. 5, when the die 5 is clamped with the cylinder liner 3 and the preform 41 arranged therein, a cavity 57, which is a predetermined amount of clearance, is formed between the small-diameter portion 44 of the preform 41 and the water-jacket forming portion 52b of the water-jacket forming die 52. Further, at the region A described above, a cavity 58, which is a predetermined amount of clearance, is formed between the small-diameter portion 44 of the preform 41 and the side die 53.

[0072] In the process of casting the cylinder block 1, 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.

[0073] The molten aluminum alloy flows through the cavity 56 formed between the lower die 54 and the side die 53, flows along the outer periphery of the small-diameter portion 44 of the preform 41, and is poured into each of the cavity 58 and the cavity 57. The cavity 58 is formed between the small-diameter portion 44 of the preform 41 and the side die 53. The cavity 57 is formed between the small-diameter portion 44 of the preform 41 and the water-jacket forming portion 52b. In addition, the preform 41 is impregnated with the molten aluminum alloy. Thus, the MMC portion is formed by the preform 41 and the aluminum alloy, and this MMC portion is used as the MMC sleeve 4. The aluminum-alloy portion located between the MMC sleeve 4 and water-jacket forming portion 52b forms a part of the cylinder barrel 21 (see FIG. 6).

[0074] The air-bubbles and aluminum-alloy oxide films contained in the molten aluminum alloy are prevented from reaching the inner portion of the preform 41, because the air-bubbles and oxide films are trapped in the portion near the outer periphery of the preform 41. Thus, the inner portion of the preform 41 is free of casting defects due to cast cavities and/or inclusion of oxide films.

[0075] Further, the molten aluminum alloy is poured into the cavity 55, formed between the water-jacket forming die 52 and the side die 53, to form the outer wall of the cylinder block 1.

[0076] In this manner, 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 sleeve 4. In this state, the aluminum alloy is cooled and solidified. Then, the dies are removed, whereby the cylinder block 1 is obtained.

[0077] FIG. 6 is a cross-sectional view taken along the plane perpendicular to the direction in which cylinders of the cylinder block 1 produced by casting method described above are aligned. As shown in FIG. 6, the upper-end portion (the deck-face portion) of the cylinder barrel 21 has only the two-layer structure including the cylinder liner 3 and the MMC sleeve 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, as in the first embodiment of the invention shown FIG. 2, only the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 is present between the cylinder bore 11 and the water jacket 12, at the deck-face portion.

[0078] Therefore, according to the second embodiment of the invention, 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, because the MMC sleeve 4 is formed on the entire outer periphery of the cylinder liner 3, the degree of closeness at which the MMC sleeve 4 and the cylinder liner are fitted to each other is uniform in the entire region in the axial direction of the cylinder liner 3. In addition, the MMC sleeve 4 and the cylinder liner 3 are reliably kept in close contact with each other over long periods.

[0079] Next, a third embodiment of the invention will be described. The third embodiment of the invention differs from each embodiment of the invention described above only in the shape of the preform 41. Accordingly, the shape of the MMC sleeve 4 in the third embodiment of the invention differs from that in each embodiment of the invention described above. The other structures and the casting method are the same as those according to each embodiment of the invention described above. Accordingly, mainly the shape of the preform 41 and the shape of the MMC sleeve 4 that is formed by the preform 41 will be described below.

[0080] As shown in FIG. 7, the preform 41 according to the third embodiment of the invention is formed such that the outer diameter of each of the upper-end portion (the deck-face portion) and the lower-end portion (the portion near the crank case) is different from the outer diameter of the other portion.

[0081] In the first embodiment of the invention, the outer diameter of the preform 41 is substantially equal to the inner diameter of the water-jacket forming portion 52b of the water-jacket forming die 52. Similarly, in the third embodiment of the invention, the outer diameter of the preform 41 at each of the upper-end portion and the lower-end portion is substantially equal to the inner diameter of the water-jacket forming portion 52b of the water-jacket forming die 52. The upper-end portion and the lower-end portion of the preform 41 will be referred to as a large-diameter portion 45 A and a large-diameter portion 45 B, respectively.

[0082] In contrast, the outer diameter of a middle portion of the preform 41, which is a portion other than the upper-end portion and the lower-end portion, is smaller than the outer diameter of each of the upper-end portion and the lower-end portion. The middle portion will be referred to as the small-diameter portion 44. As shown in FIG. 7, when the die 5 is clamped with the cylinder liner 3 and the preform 41 arranged therein, the cavity 57, which is a predetermined amount of clearance, is formed between the small-diameter portion 44 of the preform 41 and the water-jacket forming portion 52b of the water-jacket forming die 52. At the region B in the FIG. 7, the cavity 58, which is a predetermined amount of clearance, is formed between the small-diameter portion 44 of the preform 41 and the side die 53.

[0083] In the process of casting the cylinder block 1, the die 5 is clamped with the cylinder liner 3 and the preform 41 fitted to each other, and the molten aluminum alloy, which is the material of the cylinder block 1, is poured, under a predetermined pressure, through the cavity 56.

[0084] After the molten aluminum flows through the cavity 56, the air-bubbles and oxide films are trapped in the lower-end portion (the large-diameter portion 45B) of the preform 41.

[0085] The molten aluminum alloy, from which the air-bubbles and the oxide films have been removed in the above-described manner, flows along the outer periphery of the small-diameter portion 44, and is poured into the cavity 58 formed between the small-diameter portion 44 and the side die 53 and the cavity 57 formed between the small-diameter portion 44 and the water-jacket forming portion 57. At the same time, the preform 41 is impregnated with the molten aluminum alloy that is free of the air-bubbles and the oxide films. Thus, the MMC portion is formed by the preform 41 and the aluminum alloy, and this MMC portion is used as the MMC sleeve 4. Also, the aluminum alloy portion that is present between the MMC sleeve 4 and water-jacket forming portion 52b forms a part of the cylinder barrel 21 (see FIG. 8).

[0086] As described above, the air-bubbles and aluminum-alloy oxide films contained in the molten aluminum alloy are prevented from reaching the inner portion of the preform 41, because the air-bubbles and oxide films are trapped in the large-diameter portion 45B that is the lower-end portion of the preform 41. Thus, the inner portion of the preform 41 is free of casting defects due to cast cavities and/or inclusion of oxide films.

[0087] Further, the molten aluminum alloy is poured into the cavity 55 formed between the water-jacket forming die 52 and the side die 53 to form the outer wall of the cylinder block 1.

[0088] The molten aluminum alloy is poured into the cavities 55, 56, 57 and 58 in the above-described manner, and the preform 41 becomes the MMC to form the MMC sleeve 4. In this state, the aluminum alloy is cooled and solidified. Then, the dies are removed, whereby the cylinder block 1 is obtained. The aluminum alloy that is poured into the cavities 55, 57 and 58 is free of casting defects due to cast cavities and/or inclusion of oxide films, because the air-bubbles and oxide films are trapped in the large-diameter portion 45B that is the lower-end portion of the preform 41.

[0089] FIG. 8 is a cross-sectional view taken along the plane perpendicular to the direction in which cylinders of the cylinder block 1 produced by casting method described above are aligned. As shown in FIG. 8, the upper-end portion (the deck-face portion) of the cylinder barrel 21 has only the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 (the portion that has become MMC and that corresponds to the large-'diameter portion 45A) 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, as in each embodiment of the invention described above, only the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 is present between the cylinder bore 11 and the water jacket 12, at the deck-face portion.

[0090] Therefore, according to the third embodiment of the invention, 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.

[0091] Next, a fourth embodiment of the invention will be described. The fourth embodiment of the invention differs from each embodiment of the invention described above only in the shape of the preform 41. Accordingly, the shape of the MMC sleeve 4 in the fourth embodiment of the invention differs from that in each embodiment of the invention described above. The other structures and the casting method are the same as those according to each embodiment of the invention described above. Accordingly, mainly the shape of the preform 41 and the shape of the MMC sleeve 4 that is formed by the preform 41 will be described below.

[0092] As shown in FIG. 9, the preform 41 according to the fourth embodiment of the invention is formed such that the outer diameter of each of the upper-end portion (the deck-face portion) and the center portion in the axial direction is different from the outer diameter of the other portions.

[0093] In the first embodiment of the invention, the outer diameter of the preform 41 is substantially equal to the inner diameter of the water-jacket forming portion 52b of the water-jacket forming^'die 52. Similarly, in the fourth embodiment of the invention, the outer diameter of the preform 41 at each of the upper-end portion (the deck-face portion) and the center portion in the axial direction is substantially equal to the inner diameter of the water-jacket forming portion 52b of the water-jacket forming die 52. The upper-end portion and the center portion of the preform 41 will be referred to as the large-diameter portion 45A and a large-diameter portion 45C, respectively.

[0094] In contrast, the outer diameter of each of the portions other than the upper-end portion and the center portion in the axial direction is smaller than the outer diameter of each of the upper-end portion and the center portion. These portions will be referred to as a small-diameter portion 44A and a small-diameter portion 44B. As shown in FIG. 9, when the die 5 is clamped with the cylinder liner 3 and the preform 41 arranged therein, the cavity 57, which is a predetermined amount of clearance, is formed between the small-diameter portion 44A of the preform 41 and the water-jacket forming portion 52b of the water-jacket forming die 52. In addition, the cavity 58, which is a predetermined amount of clearance, is formed between the small-diameter portion 44B of the preform 41 and the side die 53.

[0095] In the process of casting the cylinder block 1, the die 5 is clamped with the cylinder liner 3 and the preform 41 fitted to each other, and the molten aluminum alloy, which is the material of the cylinder block 1, is poured, under a predetermined pressure, through the cavity 56.

[0096] The molten aluminum alloy flows through the cavity 56, flows along the outer periphery of the small-diameter portion 44B of the preform 41, and is poured into the cavity 58 formed between the small-diameter portion 44B and the side die 53 and the cavity 55 formed between the water-jacket forming die 52 and the side die 53 to form the outer wall of the cylinder block 1.

[0097] The air-bubbles and aluminum-alloy oxide films contained in the molten aluminum alloy are trapped in the large-diameter portion 45C of the preform 41. The large-diameter portion 45C is impregnated with the molten aluminum alloy. The molten aluminum alloy passes through the large-diameter portion 45C, flows along the outer periphery of the small-diameter portion 44A, and is poured into the cavity 57 formed between the small-diameter portion 44 A and the water-jacket forming portion 52B. Further, the inner portion of the preform 41 is impregnated with the molten aluminum alloy. Thus, the MMC portion is formed by the preform 41 and the aluminum alloy, and this MMC portion is used as the MMC sleeve 4. Also, the aluminum alloy portion present between the MMC sleeve 4 and water-jacket forming portion 52b forms a part of the cylinder barrel 21 (see FIG. 10).

[0098] As described above, the air-bubbles and oxide films contained in the molten aluminum alloy are trapped in the large-diameter portion 45C of the preform 41. Accordingly, the aluminum alloy poured into the preform 41 and the cavity 57 is free of casting defects due to cast cavities and/or inclusion of oxide films.

[0099] The molten aluminum alloy is poured into the cavities 55, 56, 57 and 58. The preform 41 becomes MMC to form the MMC sleeve 4. In this state, the aluminum alloy is cooled and solidified. Then, the dies are removed, whereby the cylinder block 1 is obtained.

[0100] FIG. 10 is a cross-sectional taken along the plane perpendicular to the direction in which cylinders of the cylinder block 1 produced by casting described above are aligned. As shown in FIG. 10, at the upper-end portion (the deck-face portion), the cylinder barrel 21 has the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 (the portion that has become MMC and that corresponds to the large-diameter portion 45A) 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, as in each embodiment of the invention described above, only the two-layer structure including the cylinder liner 3 and the MMC sleeve 4 is present between the cylinder bore 11 and the water jacket 12, at the deck-face portion.

[0101] Therefore, according to the fourth embodiment of the invention, 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.

[0102] 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 formed by impregnating a cylindrical porous body with a cylinder block material is fitted on an entire outer periphery of the cylinder liner, at a deck-face portion of the cylinder block, an inner periphery of the cylinder liner faces the cylinder bore, and an outer periphery of the metal matrix composite body faces the water jacket, and the outer periphery of the cylinder liner and an inner periphery of the metal matrix composite body are kept in close contact with each other.

2. The cylinder block according to claim 1, characterized in that a casting process is performed with the porous body fitted on the entire outer periphery of the cylinder liner, 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.

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 entire outer periphery 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 a deck-face portion of the cylinder block.

4. The cylinder block according to any one of claims 1 through 3, characterized in that a cross-section of the porous body, the cross-section being perpendicular to an axis of the porous body, is uniform in shape throughout the porous body in an axial direction of the porous body, and a substantial entirety of an inner peripheral side of the water jacket, which is formed on an outer peripheral side of the cylinder bore, faces the metal matrix composite body.

5. The cylinder block according to any one of claims 1 through 3, characterized in that a portion of the porous body, which is other than the deck-face portion in the porous body, is formed as a small-diameter portion that has an outer diameter smaller than an outer diameter of the deck-face portion in the porous body, and the cylinder block material is present on an outer periphery of the small-diameter portion.

6. The cylinder block according to any one of claims 1 through 3, characterized in that a portion of the porous body, which is other than the deck-face portion in the porous body and a lower-end portion of the porous body, the lower-end portion being farthest from the deck-face in the porous body, is formed as a small-diameter portion that has an outer diameter smaller than an outer diameter of each of the deck-face portion and the lower-end portion in the porous body, and the cylinder block material is present on an outer periphery of the small-diameter portion.

7. The cylinder block according to any one of claims 1 through 3, characterized in that portions of the porous body, which are other than the deck-face portion in the porous body and a center portion that is present between the deck-face portion and a lower-end portion of the porous body, the lower-end portion being farthest from the deck-face in the porous body, are formed as small-diameter portions each of which has an outer diameter smaller than an outer diameter of each of the deck-face portion and the center portion in the porous body, and the cylinder block material is present on an outer periphery of the small-diameter portion that is proximal to the deck-face.

8. 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, characterized by comprising: closely fitting a cylindrical porous body on an entire outer periphery of the cylinder liner; clamping dies together with a bore pin closely fitted in the cylinder liner and a water-jacket forming die closely fitted on an outer periphery of the porous body; and incorporating the cylinder liner and the porous body within the cylinder block by die-casting.

9. The method according to claim 8, further comprising: heating the cylinder liner and the porous body with the cylindrical porous body closely fitted on the entire outer periphery of the cylinder liner; and clamping, after heating the cylinder liner and the porous body, the dies together with the bore pin closely fitted in the cylinder liner and the water-jacket forming die closely fitted on the outer periphery of the porous body.