EP0882534A1

EP0882534A1 - Production method for a cylinder block of an internal combustion engine

Info

Publication number: EP0882534A1
Application number: EP98109853A
Authority: EP
Inventors: Manabu Fujine; Hikohito Yamazaki; Yoshiaki Kajikawa; Masayuki Hasebe; Masuo Shimizu; Mitsuhiro Karaki
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1997-06-02
Filing date: 1998-05-29
Publication date: 1998-12-09
Anticipated expiration: 2018-05-29
Also published as: JPH1147913A; EP0882534B1; DE69809126D1; DE69809126T2

Abstract

A production method for a cylinder block of an internal combustion engine includes a first step and a second step. At the first step, a preform (2) having an inside surface (2a) and an outside surface (2b) is set to a bore core (1) so that a clearance (8) is formed between the inside surface (2a) of the preform and an outside surface (1a) of the bore core (1). At the second step, a molten metal (5) is supplied into a cavity (4) so that the molten metal (5) infiltrates into the preform (2) from both the inside surface (2a) and the outside surface (2b) of the preform (2) thereby changing to a metal matrix composite, which constitutes an inside surface of a cast cylinder block.

Description

The present invention relates to a production method of a cylinder block of an internal combustion engine. More particularly, the present invention relates to a cylinder block having a cylinder bore surface constructed from metal matrix composite (MMC).

As illustrated in FIG. 11, a conventional production method for MMC cylinder block includes the steps of: setting a preheated preform (or formed member) 102 having a tapered inside surface and a straight outside surface parallel to an axis of the preform onto a bore core 101 having a tapered outside surface; arranging the bore core such that it is mounted in a cavity 104 defined by a mold 103; injecting molten metal 105 from an injection cylinder 106; and pressing the injected molten metal by a plunger 107, whereby the molten metal is infiltrated (or impregnated) into the preform 102 from the outside surface of the preform 102 only so that the preform changes to an MMC. After solidified, the cylinder block cast product is taken out of the mold 103 and the bore core 101, and then the MMC cylinder bore surface is machined to a specified diameter to form a straight cylindrical cylinder bore.

However, the conventional production method for MMC cylinder block has the following problems:

First, in the conventional production method as illustrated in FIG. 12, there is a clearance 108 between the bore core 101 and the preform 102. The clearance is caused, for example, by a difference between the taper angle of the bore core 101 and the taper angle of the preform 102 and a difference between the temperature of the bore core (for example, 100 - 200 °C) ad the temperature of the preform (for example, 500 - 900 °C). In a state where the clearance 108 exists, when the molten aluminum is pressed and is infiltrated into the preform 102 as illustrated in FIG. 13A, cracks such as crack 109 often develop in the preform 102 as illustrated in FIG. 13B. More particularly, when circumferential stress in the preform that is caused by a radial compression force acting on the outside surface of the preform exceeds an allowable shear stress, a shear fracture 109 develops along a direction inclined by 45 degrees from the direction of the compression force. Buckling occurs along the fracture surface and causes a local portion of high density of reinforcement fibers. When a piston-ring slidably contacts that high density portion during actual engine operation, abrasive wear of the piston-ring increases.

Second, the preform 102 is usually manufactured by dipping an air permeable cylindrical former into a slurry containing reinforcement fibers and particles and aspirating the slurry water from an interior of the former thereby forming a layer of the reinforcement fibers and particles on the outside surface of the former. Then, the former and the layer of the reinforcement fibers and particles are taken out of the slurry and the layer of the reinforcement fibers and particles is dried to form a preform 102 constructed from the reinforcement fibers and particles. In the preform 102, the reinforcement fibers extend in directions perpendicular to a radial direction of the preform to form a laminar wall. As a result, the separation resistant strength of one layer from another layer of the laminar wall of the preform is relatively low. As a result, the crack 109 tends to change the propagation direction to the circumferential direction of the preform due to the shear stress thereby resulting in a circumferential crack 110 (FIG. 14). When the molten aluminum flows into the crack 110 and solidifies, and when the crack portion is exposed to the outside during machining, it causes a portion 111 that has no reinforcement fibers. Such portion 111 will cause excessive abrasive wear and seizure of the piston-ring during actual operation of the engine.

Third, since the preform 102 is in plane contact with the bore core 101 when it is set to the mold, the temperature of the preform 102 rapidly decreases. As a result, the molten aluminum does not tend to infiltrate smoothly into the preform and the pressure of the molten aluminum rises before the entire portion of the preform is infiltrated with the molten aluminum, whereby the non-infiltrated portion of the preform is compressed (or crushed). For smoothly removing the preform from the former, the inside surface of the preform is tapered (more than 1 degree). Therefore, as illustrated in FIG. 16, the lower the preform is in the axial direction, the larger the deformation of the preform is due to compression. When the inside surface of such a deformed preform is machined, an aluminum portion that has no reinforcement fibers tends to be exposed to the outside. The exposed portion will cause an excessive abrasive wear and seizure of a piston-ring during actual operation of the engine.

An object of the present invention is to provide a production method for a cylinder block of an internal combustion engine having a cylinder bore surface constructed from metal matrix composite (MMC) that can solve at least one of the above-described three problems: the occurrence of a shear crack, a circumferential propagation of the shear crack, and compression of a portion of the preform.

The above-described object is achieved by the following present invention:

A production method for MMC cylinder block of an internal combustion engine according to the present invention includes the steps of: setting a generally cylindrical preform having an inside surface and an outside surface in a cavity defined by a mold and a bore core having an outside surface to form a clearance where molten metal is lead between the inside surface of the preform and the outside surface of the bore core; and supplying molten metal into the cavity so that the molten metal is infiltrated into the preform from both the inside surface and the outside surface of the preform whereby the preform changes to a metal matrix composite.

The preform is supported by an upper mold and a lower mold, or is supported by the bore core at the protrusions formed in the bore core.

In the above-described cylinder block, since the pressure of the molten aluminum is imposed on both the inside surface and the outside surface of the preform, the pressure imposed on the preform is balanced. As a result, cracks due to shear forces will not develop in the preform and circumferential propagation of such shear cracks will not occur. Further, since the molten aluminum infiltrates the preform from both the inside surface and the outside surface of the preform, the entire portion of the preform is easily infiltrated with the molten aluminum, and there will be no compression of the non-infiltrated portion of the preform. Furthermore, since the infiltration speed is high, the preheating temperature of the preform is allowed to be lower than that of the conventional process.

Since the preform line-contacts the protrusions of the bore core or the upper and lower molds, the decrease in temperature of the preform is suppressed.

The above and other objects, features, and advantages of the present invention will become more apparent and will be more readily appreciated from the following detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings, in which:

FIG. 1A is a cross-sectional view of a mold and a preform at a first step (a step for setting the preform) of a production method for a cylinder block, applicable to any embodiment of the present invention;

FIG. 1B is a cross-sectional view of the mold and the preform at a second step (a step for pouring molten metal) of the production method for a cylinder block, applicable to any embodiment of the present invention;

FIG. 1C is a cross-sectional view of the mold and the MMC layer at a third step (a step for removing a cast product from the mold and the bore core) of the production method for a cylinder block, applicable to any embodiment of the present invention;

FIG. 1D is a cross-sectional view of the mold and the MMC layer at a fourth step (a step for machining a cylinder bore surface of the cast product) of the production method for a cylinder block, applicable to any embodiment of the present invention;

FIG. 2 is a graph of molten metal pressure versus time, applicable to any embodiment of the present invention;

FIG. 3 is a cross-sectional view of an apparatus for conducting a method according to a first embodiment of the present invention;

FIG. 4 is a plan view of the apparatus of FIG. 3 viewed in direction P;

FIG. 5 is a cross-sectional view of an apparatus for conducting a method according to a second embodiment of the present invention;

FIG. 6 is an oblique view of a bore core for conducting a method according to a third embodiment of the present invention;

FIG. 7 is a cross-sectional view of an apparatus for conducting a method according to a fourth embodiment of the present invention;

FIG. 8 is a cross-sectional view of a portion of an apparatus for conducting a method according to a fifth embodiment of the present invention;

FIG. 9 is a cross-sectional view of a bore core having protrusions for conducting a method according to a sixth embodiment of the present invention;

FIG. 10 is a partial, cross-sectional view of the bore core and the protrusion of FIG. 9;

FIG. 11 is a cross-sectional view of an apparatus for conducting a conventional production method for a cylinder block;

FIG. 12 is a cross-sectional view of a bore core and a preform for conducting the conventional method;

FIG. 13A is a cross-sectional view of a portion of the preform on which a compression force is imposed;

FIG. 13B is a cross-sectional view of the portion of the preform where a crack due to a shear force is caused;

FIG. 14 is a cross-sectional view of a portion of a preform where a circumferential crack is caused;

FIG. 15 is an oblique view of a portion of the preform where a circumferential crack is caused and is exposed to outside when machined; and

FIG. 16 is a cross-sectional view of a portion of a cast cylinder block illustrating a compression of the preform.

FIGS. 1A - 1D and FIG. 2 illustrate a production method for a cylinder block of an internal combustion engine applicable to any embodiment of the present invention; FIGS. 3 - 4 illustrate a method according to a first embodiment of the present invention; FIG. 5 illustrates a method according to a second embodiment of the present invention; FIG. 6 illustrates a method according to a third embodiment of the present invention; FIG. 7 illustrates a fourth embodiment of the present invention; FIG. 8 illustrates a fifth embodiment of the present invention; FIGS. 9 and 10 illustrate a sixth embodiment of the present invention. Portions common or similar to all of the embodiments of the present invention are denoted with the same reference numerals throughout all of the embodiments of the present invention.

First, portions common or similar to all of the embodiments of the present invention will be explained with reference to FIGS. 1A - 1D and FIG. 2.

A production method for a cylinder block of an internal combustion engine according to the present invention includes a first step and a second step.

At the first step, as illustrated in FIG. 1A, a generally cylindrical, preheated, preform 2 having an inside surface 2a and an outside surface 2b is set in a cavity 4 defined by a mold 3 which includes a bore core 1 having an outside surface 1a so that a clearance 8 where molten metal is lead is formed between the inside surface 2a of the preform 2 and the outside surface 1a of the bore core 1. In order that molten metal can smoothly flow in the clearance 8, it is preferable that the clearance 8 has a thickness equal to or greater than 0.5 mm. The clearance 8 is formed throughout an entire circumference of the inside surface of the preform 2, except portions where protrusions contact the bore core 1 in a case where the preform is supported by the bore core.

At the second step, as illustrated in FIG. 1B, molten metal 5 (molten aluminum) is supplied into the cavity 4 so that the molten metal 5 is infiltrated into the preform 2 from both the inside surface 2a and the outside surface 2b of the preform 2 whereby the preform 2 changes to a metal matrix composite (MMC).

As illustrated in FIGS. 1C and 1D, the production method for a cylinder block according to the present invention may include a third step and a fourth step.

At the third step, as illustrated in FIG. 1C, a cylinder block cast product 9 is taken out of the mold 3 and the bore core 1 after the molten metal has solidified.

At the fourth step, as illustrated in FIG. 1D, a cylinder bore surface of metal matrix composite of each cylinder bore of the cylinder block cast product 9 is machined to a specified diameter.

In FIGS. 1A - 1D, the molten metal is injected into the cavity 4 by an injection cylinder 6 having a plunger tip 7. Though the bore core 1 and the preform 2 are arranged laterally in the molding apparatus, the bore core 1 and the preform 2 may be arranged vertically. The molten metal is, for example, molten aluminum, though the molten metal is not limited to molten aluminum.

The preheating temperature of the preform 2 may be lower than that of the conventional one. More particularly, while the preheating temperature of the conventional method was about 700 °C when the preform was taken out of the preheating furnace or was set to the mold, the preheating temperature of the preform 2 according to the present invention is equal to or higher than 300 °C and lower than 700 °C. Though the temperature of the bore core 1 is lower than the temperature of the preform and is, for example, 100 - 200 °C, since a decrease in the temperature of the preform 2 is delayed due to the clearance 8 between the preform 2 and the bore core 1, the temperature of the preform 2 can be relatively low.

FIG. 2 illustrates a relationship between a change in the pressure of the molten metal and beginning and completion of the infiltration of the molten metal into the preform during the second step. During a certain period of time A when the molten metal is being supplied into the cavity, the pressure of the molten metal in the cavity almost does not increase. At the time B when the molten metal has just filled the cavity, the pressure of the molten metal in the cavity begins to increase suddenly. At the time C when the pressurizing has been completed, the pressure of the molten metal in the cavity is about 750 - 850 kg/cm² (73.5 - 83.3 MPa). At an early stage of the pressure increasing period of time from the point B, infiltration of the molten metal into the preform 2 will be completed. In the case where the pressure of the molten metal is imposed on the preform from a radially outside surface of the preform, like in the conventional method, a crack due to a shear force will occur at about 3 kg/cm² (0.294 MPa). In contrast, in the present invention, since the pressures acting on the outside surface and the inside surface balance or almost balance with each other, a crack due to a shear force does not happen throughout the pressure increasing period from point B to point C in FIG. 2.

Effects of the above-described portion common or similar to all of the embodiments of the present invention will be explained.

Since the clearance 8 between the preform 2 and the bore core 1 is formed throughout the entire circumference of the preform 2, the pressure of the molten metal is imposed on both the inside surface 2a and the outside surface 2b of the preform 2. Since the pressures acting on the inside and outside surfaces of the preform 2 balance with each other, no crack due to a shear force is caused to occur unlike the conventional case where a shear crack 109 shown in FIG. 13B is caused along a plane inclined by 45 degrees from the circumferential direction of the preform.

Further, a circumferential crack 110 shown in FIG. 14 that initiates at an end of the propagating shear crack will not be caused to occur because the shear crack itself does not occur and because the preform 2 is pressed from both the inside and outside surfaces of the preform and therefore no separating force acting between the layers of the reinforcement fibers will result.

Furthermore, unlike the conventional case, a radially inner portion of the preform is unlikely to be crushed. The reason is as follows:

Generally, if the preform has enough strength to endure a pressure equal to or greater than the pressure at the time when infiltration of the molten metal into the preform has just been completed, crushing of the preform will not occur. However, in the case of the conventional method, since the pressure at the time when infiltration of the molten metal into the preform has just been completed is high, it is difficult to prevent crushing of the preform. More particularly, when the molten metal is infiltrating the preform, the temperature of the tip portion of the molten metal will be decreased so that the viscosity of the tip portion of the molten metal will be increased. A portion close to the bore core, of the preheated preform is cooled by the bore core and the decrease in temperature of the molten metal at that portion of the preform close to the bore core is large. The molten metal will solidify at that portion of the preform so that a large pressure of the molten metal will act on the radially inner portion of the preform.

In contrast, with the method according to the present invention, due to the clearance 8 provided between the bore core 1 and the inside surface of the preform 2, the following effects are caused:

(1) Because the preform 2 does not contact the bore core 1 or a contact surface of the preform 2 with the bore core 1 is minimized, the temperature of the preheated preform 2 is unlikely to decrease easily;

(2) Because the molten metal infiltrates into the preform 2 from both of the inside and outside surfaces of the preform 2, the distance by which the molten metal has to infiltrate into the preform before crushing of the preform begins is allowed to be a half of that of the conventional case.

(3) Because the molten metal infiltrates into the preform from not only the outside surface but also the inside surface of the preform, the surface area through which the molten metal infiltrates into the preform is increased. As a result, the molten metal can easily infiltrate into the preform and a distance by which the molten metal infiltrates into the preform can be large.

Because of these reasons, compression of the preform is unlikely to occur.

Portions unique to each embodiment of the present invention will now be explained.

With the first embodiment of the present invention, as illustrated in FIGS. 3 and 4, at the first step, the preform 2 is supported by and squeezed between a fixed mold 3a and a movable mold 3b of the mold 3. The preform 2 does not contact the bore core 1, and the clearance 8 is formed throughout the entire circumference of the preform 2. The fixed mold 3a includes a cylinder block journal forming portion 3c having opposite surfaces. In order to introduce the molten metal 5 (see FIGS. 1A and 1B) into the clearance 8, an opening 3d for introducing a portion of the molten metal 5 to the clearance 8 inside of the preform 2 is formed between an upper end of each of the opposite surfaces of the cylinder block journal forming portion 3c and a lower end of the inside surface of the preform 2. The bore core 1 is supported by the movable mold 3b and is moved together with the movable mold 3b.

An effect of the first embodiment of the present invention is as follows:

With the conventional method where a preform 2 is supported by a bore core 1, there are various problems. More particularly, if a foreign substance is attached to the bore core 1, the preform 2 may not be able to be set onto the bore core 1. If the molten metal cannot enter the clearance formed between the bore core 1 and the preform 2, the preform 2 may be destroyed. If the clearance is too small, the preform may be destroyed during setting. In contrast, in the present invention, because the preform 2 is supported by the movable mold 3b and the fixed mold 3a, the above-described problems are solved.

With the second embodiment of the present invention, as illustrated in FIG. 5, the bore core 1 has at least one protrusion 11 which protrudes radially outwardly from the outside surface 1a of the bore core 1 and which is integral with the bore core 1. At the first step, the preform 2 is supported by the bore core 1 at the protrusion 11. The preform 2 and the protrusion 11 line-contact or point-contact with each other. The clearance 8 is interrupted at the protrusion 11. The shape of the protrusion 11 is selected not to prevent the molten metal from filling the clearance 8.

With an effect of the second embodiment of the present invention, since the preform 2 is supported by the bore core 1 via the protrusion 11, it is easy to control the thickness of the clearance 8. As a result, the thickness of the clearance 8 can be controlled to about 0.5 mm which is a minimum thickness to ensure smooth filling of the molten metal, whereby the amount of machining of the cylinder bore after casting is minimized.

With the third embodiment of the present invention, as illustrated in FIG. 6, the bore core 1 has a plurality of protrusions which protrude from the outside surface 1a (FIG. 3) of the bore core and which are integral with the bore core 1. The protrusions extend in an axial (longitudinal) direction of the bore core 1. At the first step, the preform 2 is supported by the bore core 1 via the protrusions 11. Preferably, the number of the protrusions is equal to or more than three. The preform and the protrusions 11 line-contact with each other.

With an effect of the third embodiment of the present invention, since the protrusions extend in the axial direction of the bore core 1, the protrusions do not prevent the molten metal from flowing in the clearance 8 in the axial direction of the bore core 1. However, each clearance portion between the protrusions has to communicate with the opening (3d in FIG. 4) for introducing the molten metal to the clearance.

With the fourth embodiment of the present invention, as illustrated in FIG. 7, the bore core 1 has at least one protrusion 11 protruding radially outwardly from the outside surface 1a of the bore core. The protrusion 11 extends in an axial (longitudinal) direction of the bore core 1.

A portion of the bore core facing a cylinder block portion between adjacent cylinder bores (a portion of the bore core facing a cylinder block portion located on a line connecting centers of adjacent cylinder bores) is necessarily provided with the at least one protrusion 11.

The at least one protrusion 11 is omitted from the outboard portion of each of outboard two bore cores of multi-bore cores arranged in a longitudinal direction of a cylinder block. At the first step, the preform 2 is supported by the bore core 1 at the at least one protrusion 11. The preform 2 and the at least one protrusion 11 line-contact with each other. There is a clearance 8 except at the at least one protrusion.

With an effect of the fourth embodiment of the present invention, when the molten metal passes through a portion of the cavity between adjacent cylinder bores, the molten metal is throttled and imposes a greater pressure on the preform 2 at the throttle portion than other portions. However, since the preform 2 is necessarily supported by the protrusion 11, fracture of the preform 2 is prevented.

In the case where the bore core 1 is provided with the protrusion 11, aluminum adheres to the tip of the protrusion 11 and, as a result, it becomes difficult to set a preform member 2 to the protrusion at the next molding cycle. Since adhesion of aluminum resulting in seizure of the mold product with the protrusions occurs due to shrinkage at solidification of the cast material, it tends to occur at the longitudinal opposite ends of the cylinder block. However, in the present invention, since the protrusions 11 at the outboard portions at the outboard bore cores are omitted, adhesion and solidification of aluminum to the protrusions is unlikely to occur.

With the fifth embodiment of the present invention, as illustrated in FIG. 8, the bore core 1 has a plurality of protrusions 11 protruding radially outwardly from the outside surface 1a of the protrusion 1. The protrusions extend in the axial (longitudinal) direction of the bore core 1. One 11' of the protrusions 11 is also provided at an outboard portion of each of outboard two bore cores of multi-bore cores arranged in a longitudinal direction of a cylinder block. The outboard protrusion 11' has a height that is lower than heights of two protrusions adjacent to the outboard protrusion 11' and that protrudes outboard from a line connecting tips of the two protrusions adjacent to the outboard protrusion 11'. At the first step, the preform 2 is supported by the bore core 1 at the protrusions 11. There is a clearance 8 except at the protrusions 11.

With an effect of the fifth embodiment of the present invention, the two outboard protrusions 11' are not used for supporting the preform 2. The protrusions 11 adjacent to the outboard protrusion 11' are used for supporting the preform 2. The outboard protrusion 11' is a dummy protrusion to which molten aluminum is caused to adhere thereby preventing much aluminum from adhering to the protrusions adjacent to the outboard protrusion 11' and preventing an excessive shrinkage force from acting on the protrusions 11 adjacent to the outboard protrusion 11'. Even if aluminum adheres to the outboard protrusion 11', since the outboard protrusion 11' is low in height, it is easy to remove the cast product from the protrusion 11' and no problem will arise during-setting a preform to the core bore at the next cycle.

With the sixth embodiment of the present invention, as illustrated in FIGS. 9 and 10, the protrusion (protruding member) 11 is formed separately from the bore core 1 and is mounted to the bore core 1 so as to be movable in a radial direction of the bore core 1. A tapered member 12 is provided between the protrusion 11 and a groove formed in the bore core 1 so as to be slidable relative to the bore core 1 and the protrusion 11. By moving the tapered member 12 in the axial direction of the bore core 1, the protrusion 11 is moved in the radial direction of the bore core 1 so that the protruding height of the protrusion 11 from the outside surface 1a of the bore core 1 is adjusted.

With an effect of the sixth embodiment of the present invention, during setting the preform 2 to the bore core 1 and during supplying the molten metal to the cavity, the protrusion 11 is adjusted to take a most protruding position. While removing the cast product from the mold and bore core 1, the protrusion 11 is adjusted to take a most receding position, whereby the removing resistance is small and the cast product can be smoothly removed.

According to the present invention, the following technical advantages are obtained:

First, since the clearance 8 is formed between the preform 2 and the core bore 1, the pressures at the inside surface and the outside surface of the preform 2 balance with each other. As a result, a crack due to a shear force is unlikely to be caused in the preform 2, and a circumferential crack initiating a tip of the shear crack will not happen. Further, the molten metal can infiltrate into the preform from the inside and outside surfaces of the preform 2, compression of a portion of the preform in the thickness direction of the preform is unlikely to occur. Furthermore, due to the clearance 8, the temperature decrease of the preform 2 is suppressed and, as a result, the preheating temperature of the preform 2 is allowed to be low compared with the conventional method.

Second, in the case where the preform is supported by the upper mold and the lower mold, the preform 2 does not contact the bore core 1. As a result, the preform 2 does not need to be tapered, and the preform 2 is allowed to be formed as thin as possible.

Third, in the case where the preform 2 is supported by the bore core 1 at the protrusion 11, the thickness of the clearance 8 can be controlled substantially exactly to a specified thickness.

Fourth, in the case where the protrusion 11 extends axially in the bore core 1, the protrusion 11 does not prevent the molten metal from flowing into the clearance 8.

Fifth, in the case where the protrusion 11 is necessarily provided at a portion of the bore core 1 facing a portion of the cylinder block between adjacent cylinder bores, when a relatively large pressure of the molten metal flowing the portion between the cylinder bores acts on the preform 2, the preform can endure the pressure.

Sixth, in the case where the protrusion 11 is not provided at the outboard portion of the outboard bore core 1, even if the cylinder block material (cast product) causes a shrinkage in the longitudinal direction of the cylinder block, sticking at the tip of the outboard protrusion does not occur.

Seventh, in the case where the outboard protrusion is formed to have a low height, sticking at the tips of the protrusions adjacent to the outboard protrusion is prevented, and sticking at the tip of the outboard protrusion itself is prevented.

Last, in the case where the protrusion is formed separately from the bore core 1 and is mounted to the bore core 1 so as to be movable in the radial direction relative to the bore core 1, by receding the protrusion during removing the cast product from the bore core 1 and the mold, sticking at the tip of the protrusion can be effectively prevented.

Claims

A production method for a cylinder block of an internal combustion engine comprising:

setting a generally cylindrical preform (2) having an inside surface (2a) and an outside surface (2b) in a cavity (4) defined by a mold (3) which includes a bore core (1) having an outside surface (1a) so that a clearance (8) where molten metal (5) is lead is formed between said inside surface (2a) of said preform (2) and said outside surface (1a) of said bore core (1); and

supplying molten metal (5) into said cavity (4) so that said molten metal (5) infiltrates said preform (2) from both said inside surface (2a) and said outside surface (2b) of said preform (2) whereby said preform (2) changes to a metal matrix composite.
A method according to claim 1 further comprising:

taking a cylinder block cast product (9) out from said mold (3) and said bore core (1) after said molten metal (5) has solidified; and

machining a cylinder bore surface of metal matrix composite of each cylinder bore (1) of said cylinder block cast product (9) to a specified diameter.
A method according to claim 1, wherein during said setting, said preform (2) is preheated to a temperature equal to or higher than 300 °C and lower than 700 °C.
A method according to claim 1, wherein during said setting, said clearance (8) has a thickness equal to or greater than 0.5 mm.
A method according to claim 1, wherein said mold (3) includes a fixed mold (3a) and a movable mold (3b) and wherein during said setting, said preform (2) is supported between said fixed mold (3a) and said movable mold (3b).
A method according to claim 5, wherein said clearance (8) is formed throughout an entire circumference of said preform (2).
A method according to claim 5, wherein said fixed mold (3a) includes a cylinder block journal forming portion (3c) having opposite surfaces, and wherein an opening (3d) for introducing a portion of said molten metal (5) to said clearance (8) inside of said preform (2) is formed between an upper end of each of said opposite surfaces of said cylinder block journal forming portion (3c) and a lower end of said inside surface of said preform (2).
A method according to claim 1, wherein said bore core (1) has at least one protrusion (11) protruding outwardly from said outside surface (1a) of said bore core (1) in a radial direction of said bore core (1), and wherein said preform (2) is supported by said bore core (1) at said at least one protrusion (11).
A method according to claim 8, wherein said clearance (8) is formed along a circumference of said preform (2) except at said least one protrusion (11).
A method according to claim 8, wherein said at least one protrusion (11) is a plurality of protrusions (11) that are spaced from each other in a circumferential direction of said bore core (1), each protrusion (11) extending in an axial direction of said bore core (1).
A method according to claim 10, wherein a total number of said plurality of said protrusions (11) per cylinder bore is equal to or more than three.
A method according to claim 8, wherein a portion of said bore core (1) facing a cylinder block portion between adjacent cylinder bores (1) is necessarily provided with said at least one protrusion (11).
A method according to claim 8, wherein said at least one protrusion (11) is omitted from an outboard portion of each of outboard two bore cores of multi-bore cores arranged in a longitudinal direction of a cylinder block.
A method according to claim 8, wherein said at least one protrusion (11) is at least two protrusions (11) in which one protrusion (11') is disposed at an outboard portion of each of two outboard bore cores of multi-bore cores arranged in a longitudinal direction of a cylinder block and wherein said outboard protrusion (11') has a height that is lower than heights of two protrusions adjacent to said outboard protrusion (11') and that protrudes outboard from a line connecting tips of said two protrusions adjacent to said outboard protrusion (11').
A method according to claim 8, wherein said at least one protrusion (11) is formed separately from said bore core (1) and wherein said at least one protrusion (11) is supported movably in a radial direction of said bore core (1) so that a protrusion height of said at least one protrusion (11) from said outside surface (1a) of said bore core (1) is changeable.