Process for Casting a Cylinder Block

1. Field of the Invention

The present invention relates to a cylinder block for an internal combustion engine and a process for casting the same.

2. Description of the Prior Art

A cylinder block for an internal combustion engine is produced by a high pressure casting process such as a die casting process. In such a case, a cylinder liner block defining cylinders in the cylinder block is formed with cylinder liners of a cylindrical shape and mounted in a cylinder barrel portion of a cylinder block body which forms a main portion of the cylinder block (see Japanese Utility Model Publication No. 28289/89).

The conventional cylinder liner block is formed mainly for the purpose of increasing the wear resistance of the cylinder in which a piston slides, but this cylinder liner block does not contribute to an increase in rigidity of the cylinder block itself and particularly to an increase in rigidity of a bearing wall which supports a crankshaft in a crank case portion of the cylinder block.

The conventional cylinder block body is formed into a complicated shape having a cylinder barrel portion including a plurality of cylinders, and a crank case portion formed with a plurality of bearing walls for supporting the crankshaft. Therefore, the cylinder block body has both thin and thick portions and hence, it is difficult to make the chilling or solidifying rate uniform over the entire region during solidification of the cylinder block. For example, a base portion of the bearing wall for supporting the crankshaft is formed thick and hence, has a volume larger than those of other portions, thereby bringing about casting defects such as sink marks due to solidification shrinkage effects.

Thus, in order to prevent such casting defects, there has been conceived an approach for partially accelerating the solidifying rate by additionally using a chiller metal portion or other partially chiller means. However, such an approach results in complicated casting equipment and process, thereby bringing about an increase in cost.

Further, in the prior art casting process, in order to form a water jacket directly surrounding an outer peripheral surface of the cylinder liner block and particularly a water jacket having an undercut portion, a core such as a sand core must be used.

Accordingly, it is a first object of the present invention to provide a new cylinder block in which a cylinder liner block not only has an intrinsic function but also contributes to an increase in rigidity of the cylinder block and, particularly, of the bearing wall of the crank case portion thereof and further to an increase in performance of an internal combustion engine and to reductions in size and cost.

To achieve the above object, according to an aspect and feature of the present invention, there is provided a cylinder block comprising a cylinder block body and a cylinder liner block mounted by casting in the cylinder block body, the cylinder liner block being formed from a material having a rigidity larger than that of the cylinder block body, and the cylinder liner block comprising a liner section mounted by casting in a cylinder barrel portion of the cylinder block body, and reinforcing wall section mounted by casting in a bearing wall of a crank case portion of the cylinder block body.

With the above arrangement, the cylinder liner block can provide not only an increased in the wear resistance of cylinders in the cylinder block, but also a substantial increase in the rigidity of the bearing walls, which contributes to reductions in vibration and noise of the cylinder block and to an increase in performance of an engine. In addition, this arrangement makes it possible to reduce the thickness of the bearing walls of the crank case portion, thereby contributing to reductions in size, weight and cost of the cylinder block.

It is a second object of the present invention to provide a new cylinder block in which a portion of the cylinder liner block mounted by casting in the cylinder block body can be utilized as a chiller metal portion during casting.

To achieve the above object, according to a second aspect and feature of the present invention, there is provided a cylinder block comprising a cylinder liner block mounted in a cylinder block body to define a plurality of cylinder bores, the cylinder liner block including cylinder liners, the adjacent cylinder liners being connected in series by a common boundary wall which is integrally provided with a chiller metal portion having a chiller fin and extending from the boundary wall, the chiller metal portion being mounted by casting in a thick wall portion of the cylinder block body.

With the above arrangement, a portion of the cylinder liner block mounted by casting in the cylinder block body can be utilized as a chilling metal during casting so as to prevent the generation of casting defects, and the chiller fin providing an anchoring effect between the cylinder block body and the cylinder liner block. Thus, it is possible to provide a multi-cylinder block having a high accuracy and a high quality at a low cost as a whole.

It is a third object of the present invention to provide a new process for casting a cylinder block, wherein a cylinder block can be formed without use of a core, even when there is an undercut portion in an outer peripheral surface of a cylinder liner block, and moreover, a cylinder block of a reduced weight and a high accuracy can be produced without charging the molten metal in unnecessary areas.

To achieve the above object, according to a third aspect and feature of the present invention, there is provided a process for casting a cylinder block comprising a hollow cylindrical cylinder liner mounted in a cylinder block body to define a cylinder bore, and a water jacket defined around an outer periphery of the cylinder liner and opened at a deck surface of the cylinder block body, the process comprising steps of: integrally and projectingly providing a seal flange around an outer periphery of a lower portion of the cylinder liner; setting the cylinder liner a mold for forming the cylinder block body; fitting the cylinder liner in a hollow cylindrical a jacket projection formed in the mold so as to mate a free end of the jacket projection to a sealing surface of the seal flange; and pouring molten metal under a pressure into a cavity defined by the mold and the cylinder liner block; thereby casting the cylinder block body with the cylinder liner mounted therein.

With the above process, it is possible to shape the water jacket in the cylinder block with a high degree of accuracy without use of a core, and to shape the water jacket opened at the deck surface without any hindrance, even if there is an undercut in the cylinder liner. Further, the molten metal need not be charged in wasteful spaces, thereby achieving reductions in weight and cost of the cylinder block itself.

The above and other objects, features and advantages of the invention will become apparent from the following description of a preferred embodiment, taken in conjunction with the accompanying drawings.

FIG. 1 is a plan view of a cylinder block according to the present invention;

FIG. 2 is a sectional view taken along a line 2--2 in FIG. 1;

FIG. 3 is a sectional view taken along a line 3--3 in FIG. 1;

FIG. 4 is a sectional view taken along a line 4--4 in FIG. ;

FIG. 5 is a front view of a quadruple wet liner block;

FIG. 6 is a partially cross-sectional plan view taken along a line 6--6 in FIG. 5;

FIG. 7 is a sectional view taken along a line 7--7 in FIG. 6;

FIG. 8 is an elevational view taken along a line 8--8 in FIG. 5;

FIG. 9 is a sectional view taken along a line 9--9 in FIG. 5;

FIG. 10 is a sectional view taken along a line 10--10 in FIG. 9;

FIG. 11 is a partially cross-sectional bottom view taken along a line 11--11 in FIG. 5; and

FIGS. 12 to 14 are views illustrating steps for casting a cylinder block in a metal mold.

The present invention will now be described by way of a preferred embodiment in connection with the accompanying drawings.

A cylinder block B.sub.c for a serial four-cylinder internal combustion engine is constructed as an open deck type having a quadruple wet cylinder liner block B.sub.L. A cylinder block body 1 forming a main portion of the quadruple wet cylinder liner block B.sub.L is made by a die-casting aluminum alloy.

The cylinder block body 1 is comprised of an upper portion, i.e., a cylinder barrel portion 1.sub.u and a lower portion, i.e., a crank case portion 1.sub.L. The upper portion 1.sub.u is provided with a quadruple barrel bore 3 opened at a deck surface 2 of the cylinder block body 1. A liner section 4 of the quadruple wet cylinder liner block B.sub.L made of cast iron which will be described hereinafter is integrally mounted, by castings in the barrel bore 3. The liner portion 4 of the cylinder liner block B.sub.L is comprised of first, second, third and fourth wet liners 4.sub.1, 4.sub.2, 4.sub.3 and 4.sub.4 connected to one another. A cylinder bore 21, in which a piston (not shown) is slidably received, is made in each of the wet liners 4.sub.1, 4.sub.2, 4.sub.3 and 4.sub.4.

A water jacket 5 is defined between an outer wall surface of the quadruple wet cylinder liner block B.sub.L and an inner wall surface of the barrel bore 3 and is opened at the deck surface 2. As usual, cooling water is circulated through the water jacket 5.

Provided in an outer wall of the cylinder barrel portion 1.sub.u are a bolt bore 6 for mounting a cylinder head (not shown) on the deck surface 2, an oil passage 7 through which lubricating oil flows, and the like.

The crank case portion 1.sub.L constituting the lower portion of the cylinder block body 1 includes left and right skirt walls 8 and 9 integrally extending from a lower portion of the cylinder barrel portion 1.sub.u, and a plurality of first, second, third, fourth and fifth bearing walls 13.sub.1, 13.sub.2, 13.sub.3, 13.sub.4 and 13.sub.5 provided to extend downwardly from constructed portions 12 between longitudinally opposite end walls 10 and 11 of the cylinder barrel portion 1.sub.u and the first to fourth wet liners 4.sub.1, 4.sub.2, 4.sub.3 and 4.sub.4 so as to integrally connect the left and right skirt walls 8 and 9 with each other. First, second, third, fourth and fifth reinforcing walls 27.sub.1, 27.sub.2, 27.sub.3, 27.sub.4 and 27.sub.5 (which will be described hereinafter) of the crank case portion 1.sub.L of the cylinder liner block B.sub.L are mounted in the bearing walls 13.sub.1, 13.sub.2, 13.sub.3, 13.sub.4 and 13.sub.5, respectively, and provided with a semi-circular bearing bore 14 for supporting a crankshaft S.sub.c of the engine, a pair of bolt bores 15 for use in mounting a bearing cap (not shown) on a lower surface thereof, and the like.

The structure of the quadruple wet cylinder liner block B.sub.L of cast iron which is integrally mounted by casting in the cylinder block of aluminum alloy during the production of the cylinder block B.sub.c in the die casting process will be described in detail with reference to FIGS. 5 to 11.

The quadruple wet cylinder liner block B.sub.L includes a liner section 4 and a reinforcing wall section 27. The liner section 4 is comprised of the first, second, third and fourth cylindrical wet liners 4.sub.1, 4.sub.2, 4.sub.3 and 4.sub.4 connected to one another, with the adjacent wet liners being connected through a common boundary wall 20 and therefore, they are formed into a so-called siamese type. The cylinder bore 21, in which the piston (not shown) is slidably received, is made in each of the wet liners 4.sub.1, 4.sub.2, 4.sub.3 and 4.sub.4.

As best shown in FIGS. 5, 8 and 9, a seal flange 22 is integrally formed on an outer periphery of a lower portion of the liner section 4 to extend over the entire periphery substantially horizontally in a direction substantially perpendicular to a cylinder axis 1--1, and an upper surface of the seal flange 22 is formed into a flat sealing surface 22.sub.1.

Longitudinal and transverse ribs 23 and 24 as a spacer and a reinforcing member are integrally provided around an outer periphery of the liner section 4 above the seal flange 22. Each of these ribs 23 and 24 are formed at a height lower than that of the seal flange 22. A plurality of reinforcing small ribs 30 are integrally provided on a portion of the liner section 4 at a location lower than the seal flange 22 to project therefrom substantially in parallel to the seal flange 22.

The reinforcing wall section 27 of the crank case portion 1.sub.L of the cylinder liner block B.sub.L is comprised of the first to fifth reinforcing walls 27.sub.1 to 27.sub.5 integrally juxtaposed to extend in parallel to one another from lower portions of the boundary walls 20 provided between the longitudinally opposite end walls 25 and 26 and the first to fourth four cylindrical wet liners 4.sub.1 to 4.sub.4 of the liner section 4. These reinforcing walls 27.sub.1 and 27.sub.5 are integrally mounted by casting in the first to fifth bearing walls 13.sub.1 to 13.sub.5, respectively. Each of the reinforcing walls 27.sub.1 to 27.sub.5 is provided at its lower surface with a bonding surface 31, the bearing bore 14 and the bolt bores 15 for bolting a bearing cap (not shown).

As shown in FIG. 10, the boundary walls 20 of the liner section 4 and the first to fifth reinforcing walls 27.sub.1 to 27.sub.5 are integrally interconnected by connecting walls 28, respectively. The connecting wall 28 is made thick in a widthwise direction so as to insure a relative large volume. A plurality of relatively long heating-absorbing chiller fins 29 are projectingly provided on an outer periphery of the connecting wall 28. The connecting wall 28 of the large volume serves as a chiller metal portion to improve the cooling rate during solidification of the molten aluminum alloy during the die casting production of the cylinder block B.sub.c of the aluminum alloy.

A metal mold for producing the cylinder block B.sub.c in the die-casting process and steps for casting the same are shown in FIGS. 12 to 14.

Referring to these Figures, the metal mold M is comprised of a stationary die 40, top and bottom movable dies 41 and 42 capable of being moved vertically toward and away from each other, and a side movable die 43 capable of being moved laterally relative to the stationary die 40. The stationary die 40 is provided with a shaping surface 40.sub.1 formed into a convex shape. The top and bottom movable dies 41 and 42 have shaping surfaces 41.sub.1 and 42.sub.1 formed thereon in an opposed relation to each other. The side movable die 43 has a shaping surface 43.sub.1 formed in an opposed relation to the shaping surface 40.sub.1 of the stationary die 40. The shaping surface 43.sub.1 has cylindrical bore pins 44 dependingly provided thereon in a longitudinal arrangement for defining the cylinder bores 21. A hollow cylindrical jacket projection 45 is integrally provided in a depending manner to surround each of the bore pins 44 with an annular clearance c left therebetween and extends to the halfway of the bore pin 44.

As shown in FIGS. 12 and 13, the cylinder bore 21 in the cylinder liner block B.sub.L is fitted over each of the bore pin 44 from the left thereof. The wet liner section 4 having the longitudinal and transverse ribs 23 and 24 projecting therefrom is fitted in the jacket projection 45. A free end of the jacket projection 45 is mated with the sealing surface 22.sub.1 of the seal flange 22. A mating surface of the jacket projection 45 is formed on the sealing surface so that the molten metal does not flow in or out between the mating sealing surfaces during the die casting.

A small gap (in a range of 0.2 to 0.3 mm) is provided between the bore pin 44 and the wet liner section 4. Outer surfaces of the longitudinal and transverse ribs 23 and 24 of the wet liner section 4 are confronted or mated with the inner peripheral surface 46 of the jacket projection 45 with a small gap (in a range of 0.2 to 0.3 mm) left therebetween. A void 48 is defined between the outer surface of the liner section 4 and the inner peripheral surface 46 of the jacket projection 45, so that the molten aluminum alloy is prevented from flowing into the void 48 by the longitudinal and transverse ribs 23 and 24.

After the first to fourth wet liners 4.sub.1 to 4.sub.4 of the liner section 4 are fitted into the bore pin 44 as described above, the top and bottom movable dies 41 and 42 are moved in a closing direction. Then, by moving the side movable die 43 in a closing direction, the metal mold M is closed as shown in FIG. 13. Thus, a cavity 49 is defined by the shaping surface of the metal mold M and the cylinder liner block B.sub.L. The molten aluminum alloy is poured under a predetermined pressure into the cavity 49 through a gate 50. If this molten alloy is cooled, the cylinder block B.sub.c is formed with the cylinder liner block B.sub.L integrally mounted by casting in an aluminum alloy matrix.

In pouring the molten alloy into the cavity 49 in the above-described casting process, the molten alloy cannot penetrate between the sealing surface 22.sub.1 of the seal flange 22 and the free end of the jacket projection 45, because jacket projection 45 is mated to the sealing surface 22.sub.1. Therefore, the void 48 with no molten alloy flowing thereinto is maintained between the jacket projection 45 and the first to fourth wet liners 4.sub.1 to 4.sub.4. After releasing of the metal mold M, this void 48 forms a portion of the water jacket 5. A radial pressure is applied to the outer peripheral surface of the jacket projection 45, as shown by arrows a in FIG. 13, by the pressurized pouring of the molten alloy into the cavity 49, but is transmitted through the liner section 4 to the bore pin 44 having a large rigidity, thereby preventing the jacket projection 45 and the wet liner section 4 from being deformed.

The first to fifth reinforcing walls 27.sub.1 to 27.sub.5 of the reinforcing wall section 27 which is the lower portion of the cylinder liner block B are mounted by casting in the first to fifth bearing walls 13.sub.1 to 13.sub.5 of the crank case portion 1.sub.L of the cylinder block body 1.

After cooling of the molten metal, the metal mold M is released, as shown in FIG. 14, and the cylinder block B.sub.c completely molded is removed from the metal mold M. Thus, the water jacket 5 opened at the deck surface 2 is formed by the jacket projection 45 and the void.

In the wet cylinder liner block B.sub.L of the iron mounted by casting in the cylinder block body 1 of aluminum alloy in the above described manner, it is possible to improve the intrinsic function of the wet liner, i.e., the wear resistance of the cylinder bore in which the piston slides, as well as to substantially increase the rigidity of the cylinder block B.sub.c itself and particularly the bearing wall 13 of the crank case portion 1.sub.L thereof and to reduce the vibration and noise of the cylinder block. It is also possible to reduce the thickness of the bearing wall, which contributes to reductions in size, weight and cost of the cylinder block B.sub.c.

In addition, it is possible to reduce the phenomenon of tightening on the crankshaft S.sub.c due to the thermal shrinkage of the cylinder block of the aluminum alloy having a high coefficient of thermal expansion, when the cylinder block B.sub.c is at a low temperature, such as at the start of the engine. This contributes to a reduction in the resistance to the rotation of the crankshaft S.sub.c, thereby substantially enhancing the performance of the engine in cooperation with the increase in rigidity of the bearing wall.

In the cylinder block B.sub.c cast in the above-described manner, the connecting portion between the bearing wall 13 and the boundary wall 20 between the adjacent cylinder bores 21 is made larger in both volume and thickness than those of the other portions of the cylinder block B.sub.c. However, the chiller metal portion 28 of the wet multiple cylinder liner 4 having the chiller fins 29 is mounted by casting into this connecting portion, as shown in FIG. 4, and therefore, the chiller metal portion 28 acts as a chilling metal during the casting, thereby accelerating the solidification of the aluminum alloy matrix therearound. Therefore, it is possible to substantially equalize the solidifying rate for the thick connecting portion to the solidifying rate for the other thinner portions, so that casting defects, such as sink marks, do not result. Moreover, it is possible to increase the anchoring effect between the chiller metal portion 28 having the chiller fins 29 and the aluminum alloy of the cylinder block B.sub.p.

In the above embodiment, the cylinder block has been described as being made of aluminum alloy, and the cylinder liner block as being made of cast iron. Alternatively, the cylinder block and the cylinder liner block may be formed by combination of other materials and in this case, the rigidity of the material for the cylinder liner block should be larger than that of the cylinder block.

In addition, although the cylinder liner block according to the present invention has been applied to the four-cylinder block in the above embodiment, it is a matter of course that the cylinder liner block according to the present invention can be applied to another multi-cylinder or single-cylinder block. Further, although the cylinder liner block according to the present invention has been constructed as the quadruple wet type, it is a matter of course that the cylinder liner block can be constructed as a multiple or single dry type.