Patent ID: 12215649

DESCRIPTION OF EMBODIMENTS

Hereinafter, one embodiment of the present invention will be described in detail below with reference to the drawings.

The overall configuration of a composite cylinder block1according to one embodiment of the present invention will be first explained below.

The composite cylinder block1includes two members: a main block body2made of a metal material; and an outer member3made of a synthetic resin material.FIGS.1to3andFIG.11show the composite cylinder block1in which the main block body2and the outer member3are assembled together;FIGS.4and5show the main block body2alone; andFIGS.6to10show the outer member3alone. The main block body2and the outer member3are separately produced and then welded into one unit by the after-mentioned heat-welding technique.

In the present illustrated embodiment, the cylinder block1is adapted for use in an in-line three-cylinder engine. As indicated by the reference sign “#1” etc. inFIG.1, three cylinders of the engine are respectively referred to as #1 cylinder, #2 cylinder and #3 cylinder in order from the right front side ofFIG.1for illustration purposes. Further, the direction parallel to a line along which the centers of the three cylinders are aligned in a row is referred to as a “cylinder row direction”; the direction parallel to the center axes of the three cylinders is referred to as a “cylinder axis direction”; and the direction perpendicular to the cylinder row direction is referred to as a “width direction”. The terms “upper”, “upward”, “lower”, “downward” and the like are used in accordance with the directions of the normal top dead center and bottom dead center. It should be noted that the present invention is not limited for use in the in-line three-cylinder engine. The “front” of the cylinder block1refers to a #1 cylinder-side with respect to the cylinder row direction, whereas the “rear” of the cylinder block1refers to a #3 cylinder-side with respect to the cylinder row direction.

The metallic main block body2is an integrated body of parts to be subjected to a load or reaction force caused by a combustion/explosion event of the engine, and is integrally formed in one piece by casting of any appropriate metal material. In one preferable embodiment, the main block body2is integrally formed by die casting of an aluminum alloy. As shown inFIGS.4and5, the main block body2includes: a lower deck11having a plate shape along a plane orthogonal to the cylinder axis direction; a base part12standing upward from an upper surface of the lower deck11; three cylinder walls13each having a cylindrical shape and standing upward from the base part12; total eight columnar parts14standing upward from the base part12; and four main bearing parts15formed on a lower surface of the lower deck11. There are cylinder bores16defined by the respective cylinder walls13. These cylinder bores16extend through the base part12to the lower surface of the lower deck11.

The lower deck11is laid substantially symmetrically in the width direction with respect to the row of the cylinders, and is shaped such that a #3 cylinder-side portion of the lower deck has a relatively large dimension in the width direction and such that a #1 cylinder-side portion of the lower deck has a relatively small dimension in the width direction (seeFIG.3). This plate-shaped lower deck11has an appropriate thickness to exhibit a required rigidity. Each of the cylinder bores16ends at the lower surface of the lower deck11. In other words, the cylinder walls13do not protrude downward from the10) lower deck11. In a final assembled state of the internal combustion engine, a crankcase constituting part (such as oil pan) is attached to the lower surface of the lower deck11.

The main bearing parts15are provided at total four positions, i.e., both front and rear end positions in the cylinder row direction and positions between the cylinders, so as to rotatably support a crankshaft of the engine. The main bearing parts15protrude downward from the lower surface of the lower deck11such that each of the main bearing parts15has a rectangular plate shape of relatively large thickness with a semicircular bearing recess15aformed in the center of a lower surface thereof. In the final assembled state, a bearing cap is attached to these main bearing parts15; and journal portions of the crankshaft are rotatably supported on the main bearing parts15via bearing metals. The lower surface of the lower deck11, except the main bearing parts15, is formed as a flat surface along one plane orthogonal to the cylinder axis direction.

The cylinder walls13have a cylindrical shape of substantially constant thickness (radial dimension). In the present illustrated embodiment, the three cylindrical cylinder walls13are arranged in a siamese configuration by being mutually connected at cylinder-to-cylinder portions thereof. In other words, the bore pitch of the cylinder walls13is set smaller than the outer diameter of the cylinder walls13. Since the main block body2is made of an aluminum alloy in the present illustrated embodiment, a cylinder liner of cast iron is inserted into, or a wear-resistant metal is sprayed onto, an inner circumferential surface of the cylinder bore16.

The base part12has a lateral surface21standing upward at a substantially right angle from the upper surface of the lower deck11and a top surface22extending in parallel with the upper and lower surfaces of the lower deck11.

The columnar parts14stand upward at a substantially right angle (i.e., along the cylinder axis direction) from the top surface22of the base part12.

The columnar parts14are provided at total eight positions, i.e., both front and rear end positions in the cylinder row direction and positions between the cylinders, in such a manner as to surround the row of the three cylinder walls13of the respective cylinders. For identification, the columnar parts14are hereinafter occasionally referred to as a first columnar part14A, a second columnar part14B, a third columnar part14C, a fourth columnar part14D, a fifth columnar part14E, a sixth columnar part14F, a seventh columnar part14G and an eighth columnar part14H, respectively, in order from the #1 cylinder side. These columnar parts are generically referred to as columnar parts14when not required to be identified. The columnar parts14are individually independent and are separate from the cylinder walls13. The columnar parts14serve as bolt bosses into which cylinder head bolts (not shown) for fixing a cylinder head onto the cylinder block1are screwed.

Six of the columnar parts14other than the first and second columnar parts14A and14B, that is, the third to eighth columnar parts14C to14H each have a simple cylindrical column shape that is circular in cross section. Bolt holes24into which the cylinder head bolts are screwed are formed in the centers of upper end regions of the third to eighth columnar parts14C to14H, respectively. Basically, the third to eighth columnar parts14C to14H are equal in diameter to one another. Since the main block body2is formed by die casting in the present illustrated embodiment, a so-called draft angle is given as needed to each of surfaces of the respective block body parts oriented along the cylinder axis direction. Thus, in the strict sense, the third to eighth circular cylindrical columnar parts14C to14H have a tapered shape with the upper end regions thereof made smaller in diameter.

Differently from the third to eighth columnar parts14C to14H, the first columnar part14A has such a shape that two parallel cylindrical columnar portions are joined at their outer circumferential regions. In other words, the first columnar part14A is in the shape of the numeral “8” when viewed in plan as shown inFIG.5and when viewed in cross section perpendicular to the cylinder axis direction. More specifically, the first columnar part14A has a main columnar portion14Aa formed with the same diameter as those of the third to eighth columnar parts14C to14H and a sub columnar portion14Ab formed with a smaller diameter than that of the main columnar portion14Aa. These main and sub columnar portions are made integral with each other. As in the case of the third to eighth columnar parts14C to14H, the main columnar portion14Aa serves as a bolt boss in which the cylinder head bolt is screwed. A bolt hole24is hence formed in the center of an upper end region of the main columnar portion14Aa. The main columnar portion14Aa is located at a position symmetric to the fourth columnar part14D with respect to the center of the #1 cylinder, that is, at such a position that the total eight cylinder bolts are evenly arranged. The sub columnar portion14Ab is located at a diagonally outer side of the main columnar portion14Aa, that is, at a side of the main columnar portion14Aa opposite from the cylinder wall13of the #1 cylinder. An oil passage25is formed in the center of the sub columnar portion14Ab along the cylinder axis direction so as to supply therethrough oil pressurized by an oil pump to the cylinder head. The sub columnar portion14Ab thus corresponds to a tube in which the oil passage25of circular cross section is defined. As mentioned above, the first columnar part14A is shaped such that the main columnar portion14Aa used as the bolt boss and the sub columnar portion14Ab used as the tube for the oil passage25are joined together at their outer circumferential regions. There remain a pair of recessed gaps14Ac between outer circumferential surfaces of these columnar portions.

Similarly to the first columnar part14A, the second columnar part14B has such a shape that two parallel cylindrical columnar portions are joined at their outer circumferential regions. In other words, the second columnar part14B is in the shape of the numeral “8” when viewed in plan as shown inFIG.5and when viewed in cross section perpendicular to the cylinder axis direction. More specifically, the second columnar part14B has a main columnar portion14Ba formed with a smaller diameter than those of the third to eighth columnar parts14C to14H and a sub columnar portion14Bb formed with a slightly smaller diameter than that of the main columnar portion14Ba. These main and sub columnar portions are made integral with each other. As in the case of the third to eighth columnar parts14C to14H, the main columnar portion14Ba serves as a bolt boss in which the cylinder head bolt is screwed. A bolt hole24is hence formed in the center of an upper end region of the main columnar portion14Ba. The main columnar portion14Ba is located at a position symmetric to the third columnar part14C with respect to the center of the #1 cylinder, that is, at such a position that the total eight cylinder bolts are evenly arranged. The sub columnar portion14Bb is located at a position in front of the main columnar portion14Ba and inward of the main columnar portion14Ba in the width direction, that is, at a position adjacent to the main columnar portion14Ba on an arc about the cylinder center of the #1 cylinder. An oil passage26is formed in the center of the sub columnar portion14Bb along the cylinder axis direction, so as to supply therethrough oil pressurized by the oil pump to the cylinder head, as in the case of the sub columnar portion14Ab of the first columnar part14A. The sub columnar portion14Bb thus corresponds to a tube in which the oil passage26of circular cross section is defined. As mentioned above, the second columnar part14B is shaped such that the main columnar portion14Ba used as the bolt boss and the sub columnar portion14Bb used as the tube for the oil passage26are joined together at their outer circumferential regions. There remain a pair of recessed gaps14Bc between outer circumferential surfaces of these columnar portions.

In the present illustrated embodiment, the second columnar part14B has a lower end region integrally continuing to the lateral surface21of the base part12; whereas the other columnar parts14(i.e. the first and third to eighth columnar parts14A and14C to14H) protrude from the top surface22of the base part12without continuing to the lateral surface21of the base part12. More specifically, the outer circumferential surface of the “8”-shaped cross-sectional second columnar part14B is formed such that an inner region of the outer circumferential surface (facing the cylinder wall13) extends upward from the top surface22of the base part12and such that an outer region of the outer circumferential surface (facing away from the cylinder wall13) extends downward across the top surface22and continues to the lower deck11.

A lower end region of the oil passage25formed through the first columnar part14A and a lower end region of the oil passage26formed through the second columnar part14B are in communication with a sub oil gallery (not shown) that is formed in the vicinity of a front end portion of the lower deck11to extend along the width direction of the main block body2. The sub oil gallery extending along the width direction is in communication with a main oil gallery27(seeFIG.11andFIG.4) that is formed on a lower lateral side of the row of the cylinder walls13to extend along the cylinder row direction. High-pressure oil (lubricant), which has been pressurized by the oil pump, is supplied to the main oil gallery27. A part of the high-pressure oil is supplied to the cylinder head side via the two oil passages25and26. Further, a part of the high-pressure oil is supplied to the bearing recesses15avia oil passages28that are formed to pass through the main bearing parts15as shown inFIG.11.

The base part12is formed to not only project outwardly with a substantially constant width from the outer contours of the three series-arranged cylinder walls13, but also project outwardly with a substantially constant width from the outer contours of the columnar parts14except the second columnar part14B. The lateral surface21of the base part12is thus shaped to extend along the outer contours of the cylinder walls13and the columnar parts14and surround the outer sides of the cylinder walls13and the columnar parts14. Basically, the lateral surface21is defined by a combination of circular cylindrical surfaces concentric to the cylinder walls13and circular cylindrical surfaces concentric to the columnar parts14.

In other words, as shown inFIG.5, the top surface22is present with a substantially constant width (as indicated by the reference sign “D1” inFIG.5) around the cylinder walls13except regions adjacent to the columnar parts14and is present with a substantially constant relatively narrow width (as indicated by the reference sign “D2” inFIG.5) around the columnar parts14. Around the first columnar part14A, the top surface22is present with a width similar to that around the other columnar parts14along the “8”-shaped cross section of the first columnar part14A. The top surface22is also present with a relatively narrow width between the columnar parts14except the second columnar part14B and the cylinder walls13adjacent thereto.

Since both of the main and sub columnar portions14Ba and14Bb of the second columnar part14B are smaller in diameter than the other columnar parts14, the top surface22is present between the second columnar part14B and the cylinder wall13with the same degree of width as the width (see D1inFIG.5) of the top surface except the regions adjacent to the other columnar parts14. On the other hand, the top surface22is not present on the outer side of the second columnar part14B.

Further, the base part12has oil drop hole defining portions31provided at three positions. Each of the oil drop hole defining portions31is rectangular-shaped in plan view. The first oil drop hole defining portion31A is located at a position between the #1 cylinder and the #2 cylinder and outward of the third columnar part14C. The second oil drop hole defining portion31B is located at a position between the #2 cylinder and the #3 cylinder and outward of the fifth columnar part14E. The third oil drop hole defining portion31C is located at a position between the fourth and sixth columnar parts14D and14F, that is, lateral to the #2 cylinder on a side of the cylinder row opposite from these two oil drop hole defining portions31A and31B. Lower-half oil drop holes32are defined in center regions of the oil drop hole defining portions31, respectively, in such a manner as to extend along the cylinder axis direction. As will be explained later, these lower-half oil drop holes32constitute parts of oil drop holes through which oil used in the cylinder head side is returned to the inside of the crankcase under its own weight. Although the opening of the lower-half oil drop hole32has a substantially rectangular cross-sectional shape elongated in the cylinder row direction as shown inFIG.5, the final oil outlet end of the lower-half oil drop hole32at the lower surface of the lower deck11is narrowed into a circular shape as shown inFIG.3.

As shown inFIGS.4and5, the oil drop hole defining portions31are provided as portions of the base part12, with heights equal to those of portions of the base part12around the cylinder walls13, such that regions of the top surface22of the base part12forming the same plane surround the lower-half oil drop holes32.

The entire top surface22of the base part12, including the regions around the cylinder walls13, the regions around the columnar parts14and the regions around the lower-half oil drop holes32, is arranged along one plane orthogonal to the cylinder axis direction. As will be explained later, the top surface22serves as a mating surface for the synthetic resinous outer member3. This top surface22is a flat surface orthogonal to the cylinder axis direction, that is, a flat surface parallel to the lower surface of the lower deck11.

The synthetic resinous outer member3is configured to constitute a water jacket for flow of coolant between the main block body2and the outer member3and to constitute an upper deck with a mating surface for the cylinder head, rather than configured to be subjected to a load or reaction force caused by a combustion/explosion event of the internal combustion engine. The outer member3is integrally formed in one piece of any appropriate synthetic resin material. In one preferable embodiment, the outer member3is formed by injection molding of a thermoplastic resin such as a fiber-reinforced resin in which a glass fiber is mixed with a polyamide resin.

As shown inFIGS.6to10, the outer member3as a whole is substantially rectangular flame- or cylindrical-shaped. Mainly, the outer member3includes: an upper deck41having a mating or boundary surface for the cylinder head; a water jacket constituting wall42constituting the water jacket by surrounding the cylinder walls13and the columnar parts14except the second columnar part14B of the main block body2; a joint flange part43protruding inwardly from a lower end of the water jacket constituting wall42; front and rear flange parts44and45defining front and rear end surfaces of the composite cylinder block1, respectively; oil drop hole defining portions46corresponding to the oil drop hole defining portions31of the main block body2, respectively; and a lower lateral wall part47surrounding the circumference of the base part12of the main block body2. As will be explained later, the outer member3is combined with the main block body2by being placed over the main block body2while installing the cylinder walls13of the main block body2in an inner circumferential side of the water jacket constituting wall42.

The upper deck41is continuous in a substantially rectangular frame shape at an upper end of the outer member3. An upper surface of the upper deck41is formed as a flat surface along one plane orthogonal to the cylinder axis direction. The upper deck41includes left and right side edge portions41aand41b, a front end edge portion41cand a rear end edge portion41d, each of which is linear in shape. A plurality of ribs41eare provided on the side edge portions41aand41bin such a manner as to extend in the width direction so that the side edge portions41aand41bare connected via these ribs to an upper portion of the water jacket constituting wall42on inner sides of the edge portions. An upper end face of the water jacket constituting wall42is formed as a portion of the upper deck41and is aligned in the same plane with the side edge portions41aand41b, the front end edge portion41cand the rear end edge portion41. The cylinder head is mounted on the upper deck41via a cylinder head gasket (not shown). As the cylinder head gasket, there can be used a composite gasket having a metal seal portion brought into contact with the metallic main block body2such as the top surfaces of the cylinder walls13and a rubber seal portion brought into contact with the synthetic resinous upper deck41.

The water jacket constituting wall42is generally shaped to, when viewed in plan, extend along the outer contours of the cylinder walls13and the columnar parts14(except the second columnar part14B) of the main block body2, and has a wall surface substantially parallel to the cylinder axis direction. More specifically, the wall surface of the water jacket constituting wall42combines total eight, relatively gently curved cylinder-facing surfaces51, three on each of the left and right sides and one each on the front and rear end sides, with seven columnar part-facing surfaces52surrounding the columnar parts14except the second columnar part14B. As shown inFIG.9, the eight cylinder-facing surfaces51, when required to be individually identified, are referred to as a first cylinder-facing surface51A, a second cylinder-facing surface51B . . . and an eighth cylinder-facing surface51H in this order from the front end side in the clockwise direction. The seven columnar part-facing surfaces52are individually identified as a first columnar part-facing surfaces52A, a third columnar part-facing surfaces52C . . . and an eighth columnar part-facing surfaces52H in conformity with the designations of the columnar parts14fitted in the columnar part-facing surfaces52. Each of the columnar part-facing surfaces52is located between adjacent two of the cylinder-facing surfaces51and is concave-shaped as a concave recessed surface with a relatively small curvature radius.

The cylinder-facing surfaces51are each positioned to, when the outer member is assembled with the main block body2, provide an adequate spacing of the order of several millimeters (that is, water jacket) between the cylinder wall13and the cylinder-facing surface51. On the other hand, the columnar part-facing surfaces52are each formed in an arc shape of slightly larger diameter than that of the columnar parts14to provide a relatively small spacing between the outer circumferential surface of the columnar part14and the columnar part-facing surface52and, when the outer member is assembled with the main block body2, be generally concentric with the columnar part14. More specifically, the third to sixth columnar part-facing surfaces52C to52F corresponding to the third to sixth columnar parts14C to14F are formed as arc surfaces of substantially semicircular cross section. The seventh and eighth columnar part-facing surfaces52G and52H corresponding to the seventh and eighth columnar parts14G and14H, which are positioned at corners of one end side of the continuous water jacket, are formed as arc surfaces of about three-quarter circular cross section larger than semicircular cross section. In other words, the seventh and eighth columnar part-facing surfaces52G and52H are formed to surround about three-quarter of the circumferences of the seventh and eighth columnar parts14G and14H. The first columnar part-facing surface52A corresponding to the first columnar part14A has a cross sectional shape extending along the outer contour of the “8”-shaped cross-sectional first columnar part14A with a slight spacing left along the entire circumference. Hence, the first columnar part14A is fitted in the first columnar part-facing surface52A with a slight spacing left around the entire circumference as shown inFIG.1.

The water jacket constituting wall42does not include a concave recessed surface (as a columnar part-facing surface) corresponding to the second columnar part14B. A second columnar part insertion hole53(seeFIGS.6and19) is formed in a tubular shape along the cylinder axis direction, at a position outward of the water jacket constituting wall42(more specifically, outward of the first cylinder-facing surface51A or eighth cylinder-facing surface51H), such that the second columnar part14B is independent of the water jacket. The second columnar part insertion hole53has a cross sectional shape extending along the outer contour of the “8”-shaped cross-sectional second columnar part14B with a slight spacing left along the entire circumference. The second columnar part insertion hole53, which is shaped in cross section according to the “8”-shaped outer contour as mentioned above, has an upper end open at the upper surface of the upper deck41and extends downward from the upper surface of the upper deck41. Accordingly, the second columnar part14B is fitted in the second columnar part insertion hole53with a slight spacing left around the entire circumference as shown inFIGS.1and2.

The joint flange part43is formed to project inwardly from the lower end of the water jacket constituting wall42and is aligned together with the lower end face of the water jacket constituting wall42along one plane orthogonal to cylinder axis direction to define an outer-member-side mating surface57. The outer-member-side mating surface57is basically shaped according to the area of the top surface22of the base part12of the main block body2. In other words, the joint flange part43projects in the shape of eaves so as to extend along the contours of the three cylinder walls13serially arranged on the top surface22of the base part12and has seven openings54corresponding to seven of the columnar parts14other than the second columnar part14B; and the outer-member-side mating surface57is defined continuously on the lower side of the joint flange part. The six openings54for the third to eighth columnar parts14C to14H are circular-shaped, whereas the opening54for the first columnar part14A is substantially “8”-shaped in cross section as in the case of the first columnar part-facing surfaces52A. The outer opening edges of the respective openings54are made continuous in the cylinder axis direction with no difference in level from the corresponding columnar part-facing surfaces52.

The outer-member-side mating surface57, which includes the lower end face of the water jacket constituting wall42and the lower surface of the joint flange part43, are provided with welding ribs56for heat welding of the synthetic resin material as shown inFIGS.7,8and10. The welding ribs56are each in the form of a bead having a constant width and protruding downward from the outer-member-side mating surface57. Herein, the welding ribs56contain: a main welding rib56aextending continuously over the entire circumference around the three cylinder walls13and the seven columnar parts14in the same manner as the contour of the water jacket constituting wall42; and arc-shaped columnar part welding ribs56brespectively extending along the inner regions of the seven openings54(in between the cylinders). The columnar part welding ribs56bare continuous to the main welding rib56a.

FIGS.10and8show the welding ribs56on the outer member3before the welding process. The height (protrusion amount) of the welding rib56is decreased by heat welding so that, in the state where the outer member3is welded to the main block body2by the welding process, the welding rib56merely remains in a slight amount.

The oil drop hole defining portions46of the outer member3are provided at three locations respectively corresponding to the oil drop hole defining portions31of the main block body2. Each of the oil drop hole defining portions46protrudes downward in a tubular form from the upper deck41. Upper-half oil drop holes58are defined in inner circumferential sides of the oil drop hole defining portions46, respectively, in such a manner as to extend along the cylinder axis direction. The upper-half oil drop holes58continue to the corresponding lower-half oil drop holes32of the main block body2, thereby defining oil drop holes from the cylinder head to the crankcase. An upper end of the upper-half oil drop hole58is open at a position between the side edge portion41a,41bof the upper deck41and the water jacket constituting wall42. A lower end of the upper-half oil drop hole58is open at the same plane as the lower end face of the water jacket constituting wall42and the lower surface of the joint flange part43such that the lower end opening has an elongated shape along the cylinder row direction as shown inFIGS.7and10. In other words, a lower end face of the oil drop hole defining portion46constitutes a part of the outer-member-side mating surface57; and the lower end of the upper-half oil drop hole58is open at the outer-member-side mating surface57. Welding ribs56of the same type as mentioned above (as oil drop hole welding ribs56c) are formed on the outer-member-side mating surface57so as to surround the upper-half oil drop holes58, respectively.

The front-side flange part44has an upper end portion continuous to the front end edge portion41cof the upper deck41, thereby defining a flange surface44a(seeFIG.6) of relatively high rigidity. Similarly, the rear-side flange part45has an upper end portion continuous to the rear end edge portion41dof the upper deck41, thereby defining a flange surface45a(seeFIG.7) of relatively high rigidity. These flange surfaces44aand45aare oriented along planes orthogonal to the cylinder row direction.

The lower lateral wall part47extends downward along the cylinder axis direction from a position on an outer circumferential side of the outer-member-side mating surface57so as to surround the circumference of the base part12of the main block body2. A lower end of the lower lateral wall part47is provided so as to, when the outer member is assembled with the main block body2, reach the vicinity of the upper surface of the upper deck41. Further, cuts are made in the lower lateral wall part47at positions corresponding to the oil drop hole defining portions46in order to avoid interference with the oil drop hole defining portions21of the main block body2.

A coolant inlet hole59(seeFIG.6) is formed in the eight cylinder-facing surface51H, which is located lateral to the #1 cylinder, such that the coolant inlet hole extends from the outer surface of the outer member3to the water jacket.

Next, the welding process of the main block body2and the outer member3and the composite cylinder block1obtained as the final product by the welding process will be explained below.

As mentioned above, the metallic main block body2and the synthetic resinous outer member3are separately produced and then joined together by a heat welding technique (that is, a sort of hot plate welding). The welding is done between the top surface22of the base part12and the outer-member-side mating surface57. In the welding process, a heater for heating is placed on the lower side of the lower deck11of the metallic main block body2. In the state where the main block body2and the outer member3are separate, the base part12is heated from the lower side by the heater. For example, the heater is of the type having a plate shape with four rectangular openings through which the main bearing parts15pass. The heater is disposed within the range that covers at least the area of projection of the base part12so as to be substantially brought into close contact with the lower surface of the lower deck11. By heating with the heater, the temperature in the vicinity of the top surface22of the base part12used as the mating surface of the main block body2is raised to an adequate temperature (e.g. about 200 to 300° C.) at which the welding ribs56of the synthetic resinous outer member3can be melted and softened. Then, the outer-member-side mating surface57is brought into close contact with the top surface22of the base part12; and the outer member is pressed against the main block body2. With this, the welding ribs56are melted so that the main block body2and the outer member3are integrally welded together into one unit. The welding ribs56thus provide a substantial seal line between the main block body and the outer member. For increase of joint force, an appropriate primer treatment may be applied in advance onto the top surface22of the base part12used as the mating surface.

In the integrally welded state, the water jacket as the passage of the coolant is defined between the cylinder walls13of the main block body2and the water jacket constituting wall42of the outer member3. The water jacket is sealed by the weld joint between the top surface22of the base part12and the outer-member-side mating surface56around the cylinder walls13. In other words, the water jacket is sealed by the welding ribs56as presented as the seal line inFIG.10. In the state where the welding has been done with the welding ribs56, the upper end surfaces of the cylinder walls13of the main block body2and the upper surface of the upper deck41of the outer member3are aligned in substantially the same plane. In view of the fact that a rubber seal is used as a seal between the upper deck41of the outer member3and the cylinder head, the upper surface of the upper deck41may be set slightly lower in position than the upper end surfaces of the cylinder walls13of the main block body2.

The seven columnar parts14other than the second columnar part14B are each situated inward the water jacket such that the coolant surrounds the outer circumference of these columnar parts14. The seal line provided by the welding ribs56extends on the outer sides of the seven columnar parts14, that is, the outer sides (i.e. the water jacket constituting wall42-sides) of the openings54and thereby seals the water jacket in the form of enclosing therewith the seven columnar parts14. Thus, the water jacket of relatively narrow width is present between the outer circumferential surfaces of the columnar parts14and the water jacket constituting wall42(columnar part-facing surfaces52) as shown in e.g.FIG.11.

On the other hand, the second columnar part14B is placed in the second columnar part insertion hole53of the outer member3and thus is isolated from the water jacket. In other words, the second columnar part14B is surrounded by the synthetic resinous wall of the second columnar part insertion hole53and is not brought into contact with the coolant. There is a slight clearance left as an air layer between the inner wall surface of the second columnar part insertion hole53and the outer circumferential surface of the second columnar part14B.

The cylinder head (not shown) is disposed on the upper surface of the upper deck41and fixed by the cylinder head bolts. The cylinder head bolts are respectively screwed into the bolt holes24of the columnar parts14. Each of the columnar parts14used as the bolt boss is continuous in linear form along the cylinder axis direction until reaching the base part12so that the load exerted in the cylinder axis direction is linearly transferred to the base part12via these columnar parts. The base part12is made thick and solid to reliably bear the load transferred from the cylinder head. The main bearing parts15are made integral with the solid base part12to reliably support the crankshaft.

Furthermore, the oil drop hole defining portions31of the main block body2and the oil drop hole defining portions46of the outer member3are coupled together in an abutting manner as shown inFIGS.1and11. The welding ribs56(56c) provided on the outer member3are melted and softened, and then, welded to the mating surface (top surface22) of the main block body2as in the case of the water jacket. With this, the lower-half oil drop hole32and the upper-half oil drop hole48are continuous to each other to define one passage as an oil drop hole. The oil drop hole is connected at an upper end thereof to an oil drop hole of the cylinder head.

As described above, the composite cylinder block1according to the present embodiment is so configured that: the metallic main block body2, which is subjected to a load or reaction force, has a minimum capacity; and many parts of the cylinder block, such as the water jacket constituting wall42, are provided as the synthetic resinous outer member3. This configuration leads to a significant weight reduction of the cylinder block.

The composite cylinder block1according to the present embodiment includes: the main block body2made of metal material; and the outer member3made of resin material and welded to the main block body2as described above. The main block body2has: the cylinder walls13defining therein the cylinder bore16; and the columnar parts14formed at a position apart from the cylinder walls13. The outer member3has: the water jacket constituting wall42defining the water jacket with the cylinder walls13; and the second columnar part insertion hole53. The second columnar part14B is placed in the second columnar part insertion hole53of the outer member3with a predetermined clearance between the second columnar part14B and the second columnar part insertion hole53of the outer member3around the entire circumference, in a state of being isolated from the water jacket, and extends to the cylinder head.

Accordingly, the cylinder block1has the effect of, at the time of welding the outer member3by heating of the main block body2, preventing interference of the thermally expanded second columnar part14B with the second columnar part insertion hole53of the outer member3. This enables easy arrangement of the outer member3at a desired position on the main block body2.

After the welding of the outer member3to the main block body2, the clearance between the inner wall surface of the second columnar part insertion hole53and the outer circumferential surface of the second columnar part14B serves as an air layer (insulating layer) in the cylinder block1. This makes it less likely that the second columnar part14B and the oil inside the oil passage26will be cooled by the coolant during engine warm-up (warm-up of the internal combustion engine), thereby improving warm-up performance.

Further, the pressure from the oil acts on the oil passages25and26. However, the oil passage25is formed in the metallic first columnar part14A; and the oil passage26is formed in the metallic second columnar part14B. Thus, the cylinder block1ensures its pressure resistance.

In the present embodiment, the second columnar part14B has: the main cylindrical columnar portion14Ba formed as the main columnar portion into which the cylinder head bolt for fixing the cylinder head is screwed; and the sub cylindrical columnar portion14Bb formed integral with the main cylindrical columnar part as the sub columnar part having formed therein the oil passage26for supplying the oil pressurized by the oil pump to the cylinder head.

The cylinder block1is thus prevented from being deformed during the casting.

Furthermore, the second columnar part14B has the pair of recessed gaps14Bc formed between the outer circumferential surfaces of the main and sub columnar portions14Ba and14Bb. By the formation of such recessed gaps14Bc, the second columnar part14B is lightened as compared with the case where the second columnar part14B is formed such that the outer shape of the cross section is elongated circular without having the pair of recessed gaps14Bc.

Thus, the cylinder block1is reduced in weight due to the formation of such recessed gaps14Bc on the second columnar part14B.

Although the present invention has been described by way of the above specific embodiment, the present invention is not limited to the above-described specific embodiment. Various changes and modifications of the above-described specific embodiment are possible.

For example, the bolt hole24may not be formed in the second columnar part14B although at least the bolt hole24is formed in the second columnar part14B in the above-described embodiment. In other words, the second columnar part14B may be of the type having only the oil passage for supplying the oil pressurized by the oil pump to the cylinder head, that is, consisting of the above-mentioned sub columnar portion14Ab or the like.

Although only the second columnar part14B among the columnar parts14is placed in the outer member3in the state of being isolated from the water jacket in the above-described embodiment, the cylinder block may be configured such that all of the columnar parts14are placed in the outer member3in the state of being isolated from the water jacket. In such a case, it suffices to configure the cylinder block such that all of the columnar parts14are placed in the outer jacket3with a predetermined clearance left between the columnar parts and the outer member3around the entire circumference, in the state of being isolated from the water jacket, and each extends to the cylinder head.