Composite cylinder block

Abstract

To enable heat-welding joining to a synthetic resinous outer member by heating a metallic main block to near a melting temperature of a synthetic resin material.SOLUTION: A compound type cylinder block of an internal combustion engine is composed of a metallic main block, and a synthetic resinous outer member, and is heat-welded on a joint surface orthogonal to a cylinder axis direction. The main block is equipped with columnar portions 14 (14A, 14C, 14E, and 14G) that become bolt boss portions of a cylinder head, and columnar opposite surfaces 52 (52A, 52C, 52E, and 52F) on the outer member side oppose to outside surfaces of the columnar portions 14 through minute clearances. Clearance dimensions has relationships of "Δ1>Δ3" and "Δ8>Δ6" so that the main block 2 does not interfere even if it thermally expands during heat-welding.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a composite cylinder block for an internal combustion engine, which is constructed by combining metal members and synthetic resin members. [Background technology]

[0002] Patent Document 1 discloses a cylinder block constructed by machining the outer wall of a water jacket surrounding a cylinder liner from a metal cylinder block cast using an aluminum alloy or the like, and combining it with a resin block having a cylindrical wall that fits around the outer surface of the cylinder liner. The machining process leaves behind the cylindrical cylinder liner and multiple pillars that become the cylinder head bolt bosses. The resin block has through holes into which the pillars fit. An adhesive layer is then applied to the outer surface of the cylinder liner and the outer surface of the pillars, and the resin block and metal block are integrated by fitting the through holes for the pillars into the cylindrical wall of the resin block. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-112147 Summary of the Invention [Problem to be solved by the invention]

[0004] In this configuration, when combining the metal cylinder block and the resin block, the multiple columnar portions must be tightly fitted into the through holes of the resin block together with the adhesive layer, so in reality, even a slight dimensional error makes assembly difficult. [Means for solving the problem]

[0005] The present invention provides a composite cylinder block comprising: a metal main block including at least a cylinder wall and a main bearing portion; and an outer member made of synthetic resin configured to surround the cylinder wall, forming a water jacket between the metal main block and the cylinder wall, and including an upper deck portion on which a cylinder head is disposed, the outer member being heat-welded to the main block by heating the main block, the main block includes a plurality of pillars that extend upright to reach an upper surface of the upper deck portion and correspond to cylinder head bolts that fix the cylinder head, the outer member has a columnar portion facing surface that faces an outer surface of the columnar portion via a small gap, The dimension along the cylinder row of the minute gap between the outer surface of each columnar portion facing outward in the cylinder row direction and the corresponding columnar portion opposing surface is set to be larger for columnar portions that are farther away from the center in the cylinder row direction.

[0006] In this configuration, when the metal main block is heated during heat welding, the metal main block thermally expands, causing the position of the columnar portion, specifically, the position of the columnar portion relative to the surface of the synthetic resin outer member facing the columnar portion, to shift in the cylinder row direction. Therefore, by setting the dimension of the minute gap along the cylinder row as described above, an appropriate gap can be secured between the columnar portions during heat welding. [Effects of the Invention]

[0007] This invention allows the individually manufactured main block and outer member to be heat-welded together without interference between the multiple pillars of the metal main block and the opposing surfaces of the resin outer member, simplifying the manufacturing process for the composite cylinder block and enabling it to be manufactured at low cost. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a composite cylinder block according to an embodiment of the present invention. [Figure 2]FIG. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] Plan view of the main block. [Figure 6] FIG. [Figure 7] FIG. 4 is a perspective view of the outer member in a state where it is turned upside down. [Figure 8] An enlarged view of a portion of Figure 7. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. 3 is a perspective view of a cross section taken along line AA in FIG. 2. [Figure 12] FIG. 3 is an enlarged explanatory view of a main part of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0010] First, the overall structure of a composite cylinder block 1 according to one embodiment will be described. The composite cylinder block 1 is composed of two members: a metal main block 2 and a synthetic resin outer member 3. Figures 1 to 3 and 11 show the composite cylinder block 1 with the main block 2 and outer member 3 integrated together, while Figures 4 and 5 show the main block 2 alone, and Figures 6 to 10 show the outer member 3 alone. The main block 2 and outer member 3 are manufactured separately and then welded together using a heat welding technique described below.

[0011] The illustrated example is a cylinder block 1 for an in-line three-cylinder engine. For ease of explanation, as indicated by the designations "#1" and so on in FIG. 1, the cylinders will be referred to as #1, #2, and #3, starting from the front right side of FIG. 1. The direction parallel to the line through which the centers of these three cylinders are aligned will be referred to as the "cylinder row direction," the direction parallel to the central axis of each cylinder will be referred to as the "cylinder axis direction," and the direction perpendicular to the cylinder row direction will be referred to as the "cylinder width direction." Terms such as "top," "upper," "lower," and "belower" will be used to refer to typical directions of top dead center and bottom dead center. Note that the present invention is not limited to in-line three-cylinder engines. Furthermore, the "front" of the cylinder block 1 refers to the #1 cylinder side in the cylinder row direction, and the "rear" refers to the #3 cylinder side.

[0012] The metal main block 2 integrates components that support the loads and reaction forces associated with combustion and explosion in an internal combustion engine. Each component is integrally cast using an appropriate metal material. In a preferred embodiment, the block is integrally cast using an aluminum alloy by die-casting. As shown in FIGS. 4 and 5 , the main block 2 includes a plate-shaped lower deck 11 extending along a plane perpendicular to the cylinder axis, a base 12 extending upward from the upper surface of the lower deck 11, three cylindrical cylinder walls 13 extending upward from the base 12, a total of eight columnar portions 14 also extending upward from the base 12, and four main bearing portions 15 provided on the underside of the lower deck 11. Each cylinder wall 13 defines a cylinder bore 16, which extends through the base 12 to the underside of the lower deck 11.

[0013] The lower deck 11 extends approximately symmetrically in the width direction around the cylinder row, with the width dimension being relatively large on the #3 cylinder side and relatively small on the #1 cylinder side (see FIG. 3). The plate-shaped lower deck 11 has an appropriate thickness to ensure the necessary rigidity. The cylinder bores 16 terminate at the lower surface of the lower deck 11. In other words, the cylinder walls 13 do not protrude below the lower deck 11. When the internal combustion engine is finally assembled, crankcase components (e.g., an oil pan, not shown) are attached to the lower surface of the lower deck 11.

[0014] The main bearings 15 are provided at four locations in the cylinder row direction, at both the front and rear ends and between the cylinders, to rotatably support the crankshaft (not shown). Each main bearing 15 is formed as a relatively thick rectangular plate that protrudes downward from the underside of the lower deck 11, and each main bearing 15 has a semicircular bearing recess 15a in the center of its underside. Bearing caps (not shown) are ultimately attached to these main bearings 15, and the crankshaft journals are rotatably supported via bearing metals (not shown). The underside of the lower deck 11, excluding the main bearings 15, is flat along a plane perpendicular to the cylinder axial direction.

[0015] The cylinder walls 13 are cylindrical and have a substantially constant thickness (radial dimension). In the illustrated example, three cylindrical cylinder walls 13 are connected to each other at the inter-cylinder portions to form a so-called Siamese structure. In other words, the bore pitch is shorter than the outer diameter of the cylinder walls 13. In the illustrated example, the main block 2 is made of an aluminum alloy, so that a cast iron cylinder liner (not shown) is inserted into the inner peripheral surface of the cylinder bore 16, or a wear-resistant metal is thermally sprayed onto the inner peripheral surface.

[0016] The base portion 12 has side surfaces 21 that rise substantially perpendicularly from the upper surface of the lower deck 11, and a top surface 22 that is parallel to the upper and lower surfaces of the lower deck 11. The columnar portions 14 each rise upward from the top surface 22 of the base portion 12 at a substantially perpendicular angle (in other words, along the cylinder axial direction).

[0017] The pillar-shaped portions 14 are provided at eight locations, including the front and rear ends of the cylinder row and between the cylinders, so that the three cylinder walls 13 surround the continuous cylinder row. Hereinafter, when it is necessary to distinguish between them, they will be referred to as the first pillar-shaped portion 14A, the second pillar-shaped portion 14B, the third pillar-shaped portion 14C, the fourth pillar-shaped portion 14D, the fifth pillar-shaped portion 14E, the sixth pillar-shaped portion 14F, the seventh pillar-shaped portion 14G, and the eighth pillar-shaped portion 14H, starting from the #1 cylinder side, as shown in FIG. 4 . When no distinction is necessary, they will be collectively referred to as pillar-shaped portions 14. Each pillar-shaped portion 14 is independent and separate from the cylinder walls 13. These pillar-shaped portions 14 function as bolt bosses onto which cylinder head bolts (not shown) are threaded for fixing a cylinder head (not shown) disposed on the cylinder block 1.

[0018] The six columnar sections 14 excluding the first columnar section 14A and the second columnar section 14B, i.e., the third columnar section 14C to the eighth columnar section 14H, each have a simple cylindrical shape with a circular cross section, and a bolt hole 24 into which a cylinder head bolt is threaded is formed at the center of the upper end. Basically, the third columnar section 14C to the eighth columnar section 14H have the same diameter. Here, in the illustrated example, because the main block 2 is cast by die-casting, a so-called draft is provided as necessary on the surface of each section along the cylinder axial direction. Therefore, strictly speaking, the third columnar section 14C to the eighth columnar section 14H, which are cylindrical, have a tapered shape with a slightly smaller diameter at the upper end.

[0019] Unlike the third to eighth columnar sections 14C to 14H, the first columnar section 14A has a shape resembling two parallel cylinders joined at a portion of their outer peripheries. In other words, in a plan view and a cross-sectional view perpendicular to the cylinder axis direction, as shown in FIG. 5, the first columnar section 14A has an "8" shape. Specifically, a main columnar section 14Aa having a diameter similar to that of the third to eighth columnar sections 14C to 14H is integrated with a sub-columnar section 14Ab having a smaller diameter. Like the third to eighth columnar sections 14C to 14H, the main columnar section 14Aa functions as a bolt boss for a cylinder head bolt and has a bolt hole 24 at the center of its upper end. This main columnar section 14Aa is located symmetrically to the fourth columnar section 14D across the center of the #1 cylinder, i.e., where a total of eight cylinder head bolts are evenly spaced. The sub-cylindrical portion 14Ab is located diagonally outside the main cylindrical portion 14Aa, that is, on the opposite side from the cylinder wall 13 of the #1 cylinder. An oil passage 25 is formed in the center of this sub-cylindrical portion 14Ab along the cylinder axial direction for supplying oil pressurized by an oil pump (not shown) to the cylinder head. In other words, the sub-cylindrical portion 14Ab corresponds to a pipe that forms the oil passage 25, which has a circular cross section. In this way, the first columnar portion 14A is formed by connecting the main cylindrical portion 14Aa, which serves as the bolt boss portion, and the sub-cylindrical portion 14Ab, which serves as the pipe for the oil passage 25, at parts of their circumferential surfaces, with a pair of recessed grooves 14Ac remaining on the outer circumferential surface between them.

[0020] The second columnar portion 14B is similar to the first columnar portion 14A and has a shape resembling two parallel cylinders joined at a portion of their outer peripheries. In other words, in a plan view and a cross-sectional view perpendicular to the cylinder axis direction, as shown in FIG. 5, it has an "8" shape. Specifically, a main columnar portion 14Ba, which has a smaller diameter than the third to eighth columnar portions 14C to 14H, is integrated with a sub-columnar portion 14Bb, which has a slightly smaller diameter than the main columnar portion 14Ba. Like the third to eighth columnar portions 14C to 14H, the main columnar portion 14Ba functions as a bolt boss for the cylinder head bolts and has a bolt hole 24 at the center of its upper end. This main columnar portion 14Ba is located symmetrically to the third columnar portion 14C across the center of the #1 cylinder, i.e., where a total of eight cylinder head bolts are evenly spaced. The sub-cylindrical portion 14Bb is located in front of and inward of the main cylindrical portion 14Ba in the width direction, i.e., adjacent to the main cylindrical portion 14Ba on an arc centered at the center of the #1 cylinder. Similar to the sub-cylindrical portion 14Ab of the first columnar portion 14A, an oil passage 26 is formed at the center of this sub-cylindrical portion 14Bb along the cylinder axial direction to supply oil pressurized by an oil pump (not shown) to the cylinder head. In other words, the sub-cylindrical portion 14Bb corresponds to a pipe constituting the oil passage 26, which has a circular cross section. Thus, the second columnar portion 14B is formed by connecting the main cylindrical portion 14Ba, which serves as the bolt boss portion, and the sub-cylindrical portion 14Bb, which serves as the pipe for the oil passage 26, at portions of their circumferential surfaces, with a pair of recessed grooves 14Bc remaining on the outer circumferential surface between them.

[0021] In the illustrated example, the second columnar section 14B is configured such that the lower portion thereof is integrated with the side surface 21 of the base section 12, whereas the other columnar sections 14 (first columnar section 14A, third columnar section 14C to eighth columnar section 14H) are not continuous with the side surface 21 of the base section 12 and protrude from the top surface 22 of the base section 12. In other words, of the outer peripheral surface of the second columnar section 14B having an "8"-shaped cross section, the inner portion (the portion facing the cylinder wall 13) rises up from the top surface 22 of the base section 12, whereas the outer portion (the portion opposite the cylinder wall 13) extends below the top surface 22 and continues to the lower deck 11.

[0022] The lower end of the oil passage 25 passing through the first columnar portion 14A and the lower end of the oil passage 26 passing through the second columnar portion 14B each communicate with a sub-oil gallery (not shown) extending in the width direction of the main block 2 and formed near the front end of the lower deck 11. This sub-oil gallery along the width direction communicates with a main oil gallery 27 (see FIGS. 11 and 4) extending in the cylinder row direction and formed on the lower side of the row of cylinder walls 13. High-pressure oil (lubricating oil) pressurized by an oil pump (not shown) is supplied to the main oil gallery 27. A portion of this high-pressure oil is supplied to the cylinder head side via two oil passages 25 and 26. As shown in FIG. 11, a portion of the high-pressure oil is also supplied to the bearing recess 15a via an oil passage 28 passing through the main bearing portion 15.

[0023] The base portion 12 is formed so as to protrude outward by a substantially constant width from the outer contours of the three cylinder walls 13 arranged in series, and is also formed so as to protrude outward by a substantially constant width from the outer contours of the columnar portions 14 excluding the second columnar portion 14B. In other words, the shape of the side surface 21 of the base portion 12 is determined so as to follow the outer contours of the cylinder walls 13 and the columnar portions 14 and surround the outside of them. Essentially, the side surface 21 is a combination of a cylindrical surface concentric with the cylinder walls 13 and a cylindrical surface concentric with the columnar portions 14.

[0024] In other words, as shown in Fig. 5, the top surface 22 exists with a substantially constant width (see symbol D1 in Fig. 5) around the cylinder wall 13 except for the portion adjacent to the columnar portion 14, and the top surface 22 exists with a relatively narrow, substantially constant width (see symbol D2 in Fig. 5) around the columnar portion 14. Around the first columnar portion 14A, the top surface 22 exists with a width similar to that of the other columnar portions 14, following the "8"-shaped cross section of the first columnar portion 14A. In addition, a top surface 22 with a relatively narrow width also exists between each columnar portion 14 except for the second columnar portion 14B and the adjacent cylinder wall 13.

[0025] As for the second columnar portion 14B, both the main columnar portion 14Ba and the sub columnar portion 14Bb have smaller diameters than the other columnar portions 14, and so a top surface 22 having a width similar to the width (see D1 in FIG. 5) of the portion other than the portion adjacent to the other columnar portions 14 exists between the second columnar portion 14B and the cylinder wall 13. On the other hand, no top surface 22 exists on the outside of the second columnar portion 14B.

[0026] Furthermore, the base portion 12 has three oil drop hole forming portions 31, each of which is rectangular in plan view. The first oil drop hole forming portion 31A is located between the #1 and #2 cylinders and is outside the third columnar portion 14C. The second oil drop hole forming portion 31B is located between the #2 and #3 cylinders and is outside the fifth columnar portion 14E. The third oil drop hole forming portion 31C is located on the opposite side of the cylinder row from the two oil drop hole forming portions 31A and 31B, between the fourth columnar portion 14D and the sixth columnar portion 14F, i.e., to the side of the #2 cylinder. Each of these oil drop hole forming portions 31 has a lower oil drop hole half 32 extending in the cylinder axial direction formed in its center. As described below, this lower oil drop hole half 32 forms a part of the oil drop hole that returns oil used in the cylinder head to the crankcase by gravity. The lower half of the oil drop hole 32 has a generally rectangular cross-sectional shape that is elongated in the cylinder row direction, as shown in Figure 5, but on the underside of the lower deck 11, which is the final oil outlet, it is narrowed to a circular hole as shown in Figure 3.

[0027] As shown in Figures 4 and 5, the oil drop hole forming portion 31 is part of the base portion 12 and has the same height as the periphery of the cylinder wall 13, etc., and a portion of the top surface 22 of the base portion 12, which forms the same plane, surrounds the periphery of the lower half of the oil drop hole 32.

[0028] The entire top surface 22 of the base portion 12, including the portion surrounding the cylinder wall 13, the portion surrounding the columnar portion 14, and the portion surrounding the lower half of the oil drop hole 32, is along a single plane perpendicular to the cylinder axial direction. As will be described later, this top surface 22 is the surface that will be joined to the synthetic resin outer member 3, and forms a plane perpendicular to the cylinder axial direction, and therefore is a plane parallel to the underside of the lower deck 11.

[0029] Next, the synthetic resin outer member 3 is not a component that supports the load or reaction force associated with combustion and explosion in the internal combustion engine, but mainly constitutes a water jacket through which cooling water flows between it and the main block 2, and also constitutes the upper deck portion that is the joint surface with the cylinder head, and is integrally formed in each part using an appropriate synthetic resin material. In one embodiment, it is integrally injection molded using a thermoplastic resin, for example, a fiber-reinforced resin made by blending glass fiber with polyamide resin.

[0030] 6 to 10, the outer member 3 has a generally rectangular frame or cylindrical shape overall. The outer member 3 primarily includes an upper deck portion 41 that serves as a joint or boundary surface with the cylinder head, a water jacket-constituting wall 42 that surrounds the cylinder wall 13 of the main block 2 and the columnar portions 14 other than the second columnar portion 14B to form a water jacket, a joint flange portion 43 that extends inward from the lower end of the water jacket-constituting wall 42, a front flange portion 44 and a rear flange portion 45 that form the front and rear end faces of the combined cylinder block 1, oil drop hole-forming portions 46 that correspond to the oil drop hole-forming portions 31 on the main block 2, and a lower side wall portion 47 that surrounds the periphery of the base portion 12 on the main block 2. As described below, the outer member 3 is assembled with the main block 2 by placing the cylinder wall 13 of the main block 2 inside the water jacket-constituting wall 42 and covering the main block 2.

[0031] The upper deck portion 41 extends from the upper end of the outer member 3 in a generally rectangular frame shape, with its upper surface being flat and aligned along a plane perpendicular to the cylinder axial direction. The upper deck portion 41 includes linear left and right side edges 41a, 41b, a front edge 41c, and a rear edge 41d. The side edges 41a, 41b are connected to the upper portion of the water jacket wall 42 located inside via several ribs 41e extending in the width direction. The upper end surface of the water jacket wall 42 forms part of the upper deck portion 41 and is aligned along a single plane together with the side edges 41a, 41b, the front edge 41c, and the rear edge 41d. A cylinder head (not shown) is mounted on the upper deck portion 41 via a cylinder head gasket (not shown). As the cylinder head gasket, for example, a composite gasket is used in which the part that comes into contact with the metal main block 2, such as the top surface of the cylinder wall 13, is a metal seal, and the part that comes into contact with the synthetic resin upper deck part 41 is a rubber seal.

[0032] In a plan view, the water jacket wall 42 has a shape that generally follows the outer contours of the cylinder wall 13 and the columnar portions 14 (excluding the second columnar portion 14B) of the main block 2, and has wall surfaces that are substantially parallel to the cylinder axial direction. More specifically, the water jacket wall 42 is configured by combining a total of eight cylinder-facing surfaces 51, three on each side of the cylinder wall 13 and three on the front and rear ends, that are relatively gently curved and face the outer circumferential surface of the cylinder wall 13 without overlapping with the columnar portions 14, and a total of seven columnar portion-facing surfaces 52 that surround the columnar portions 14 other than the second columnar portion 14B. As shown in FIG. 9 , when it is necessary to individually distinguish the eight cylinder-facing surfaces 51, they are referred to as the first cylinder-facing surface 51A, the second cylinder-facing surface 51B, to the eighth cylinder-facing surface 51H, in clockwise order from the front end. The seven columnar portion facing surfaces 52 are individually distinguished as a first columnar portion facing surface 52A, a third columnar portion facing surface 52C, to an eighth columnar portion facing surface 52H, in accordance with the names of the columnar portions 14 inserted therein. Each columnar portion facing surface 52 is located between two adjacent cylinder facing surfaces 51, and has a concave shape as a concave groove surface with a relatively small radius of curvature.

[0033] 1, the position of the cylinder-opposing surface 51 is set so that, when combined with the main block 2, an appropriate gap (in other words, a water jacket) of, for example, about several millimeters is formed between the cylinder-opposing surface 51 and the cylinder wall 13. In contrast, the columnar-portion-opposing surface 52 forms an arcuate surface with a diameter slightly larger than that of each columnar portion 14 so that a relatively small gap is formed between the columnar-portion-opposing surface 52 and the outer circumferential surface of each columnar portion 14, and is configured to be approximately concentric with each columnar portion 14 when combined with the main block 2. More specifically, the third columnar-portion-opposing surfaces 52C to 52F corresponding to the third columnar portion 14C to the sixth columnar portion 14F each form a cylindrical surface with a substantially semicircular cross section. The seventh columnar-section facing surfaces 52G and 52H corresponding to the seventh columnar section 14G and the eighth columnar section 14H are located at corners of the continuous water jacket, forming cylindrical surfaces with cross sections measuring approximately three-quarters of a circle, which is larger than a semicircle. In other words, approximately three-quarters of the circumference of the seventh columnar section 14G and the eighth columnar section 14H is surrounded by the seventh columnar-section facing surfaces 52G and 52H. The first columnar-section facing surfaces 52A corresponding to the first columnar section 14A have a cross-sectional shape that follows the outline of the figure "8" so that a small gap remains around the entire circumference, corresponding to the first columnar section 14A whose cross section is shaped like the figure "8." This allows the first columnar section 14A to fit within the first columnar-section facing surfaces 52A with a small gap remaining around the entire circumference, as shown in FIG. 1 .

[0034] The second columnar portion 14B does not have a corresponding recessed groove portion (columnar portion-facing surface) in the water jacket constituent wall 42. For the second columnar portion 14B, a second columnar portion insertion hole 53 is formed in the shape of a conduit extending in the cylinder axial direction on the outside of the water jacket constituent wall 42 (more specifically, the first cylinder-facing surface 51A to the eighth cylinder-facing surface 51H) so as to be independent from the water jacket (see FIGS. 6 and 10). The second columnar portion insertion hole 53 has a cross-sectional shape that follows the outline of the figure "8" so that a small gap remains around the entire circumference, corresponding to the second columnar portion 14B, which has an "8"-shaped cross section. The second columnar portion insertion hole 53, which has a cross-sectional shape that follows the outline of the figure "8," opens at its upper end to the top surface of the upper deck portion 41 and extends downward from there. As a result, as shown in FIGS. 1 and 2, the second columnar section 14B fits into the second columnar section insertion hole 53, leaving a small gap all around the circumference.

[0035] The joining flange portion 43, which protrudes inward from the lower end of the water jacket constituent wall 42, is formed along a plane perpendicular to the cylinder axial direction together with the lower end surface of the water jacket constituent wall 42, and constitutes an outer member-side joining surface 57. This outer member-side joining surface 57 basically has a shape corresponding to the area of ​​the top surface 22 of the base portion 12 of the main block 2. That is, the joining flange portion 43 protrudes like an eave so as to follow the contours of the three cylinder walls 13 connected in series on the top surface 22 of the base portion 12, and is provided with seven openings 54 corresponding to the seven columnar portions 14 excluding the second columnar portion 14B, and the outer member-side joining surface 57 is formed continuously on the lower surfaces of these openings. The six openings 54 for the third columnar portion 14C to the eighth columnar portion 14H are circular, and the opening 54 for the first columnar portion 14A is generally shaped like an "8," similar to the first columnar portion-facing surface 52A. The outer edge of each opening 54 is continuous with the corresponding columnar portion facing surface 52 in the axial direction of the cylinder without any step.

[0036] 7, 8, and 10, a bead-like welding rib 56 of a certain width protruding downward from the outer member-side joining surface 57 is formed on the outer member-side joining surface 57, which includes the lower surface of the water jacket constituent wall 42 and the lower surface of the joining flange portion 43, for heat welding of a synthetic resin material. The welding rib 56 includes a main welding rib 56a that is continuous around the entire circumference, passing around the outside of the three cylinder walls 13 and the seven columnar portions 14, similar to the outline of the water jacket constituent wall 42, and arc-shaped columnar portion welding ribs 56b that respectively fit along the inside portions of the seven openings 54 (portions that fit between the cylinders), and the columnar portion welding ribs 56b are continuous with the main welding rib 56a.

[0037] 10 and 8 show the welding ribs 56 on the outer member 3 before welding. When the outer member 3 is joined to the main block 2 through the welding process, the welding ribs 56 are heated and melted, reducing their height (amount of protrusion) and leaving only a small portion remaining.

[0038] The oil drop hole forming portions 46 of the outer member 3 are provided at three locations on the outer member 3 to correspond to the oil drop hole forming portions 31 on the main block 2. Each oil drop hole forming portion 46 protrudes downward from the upper deck portion 41 in a duct-like shape, and an upper oil drop hole half 58 extending in the cylinder axial direction is formed on the inner periphery. This upper oil drop hole half 58 is continuous with the lower oil drop hole half 32 on the main block 2 to form an oil drop hole extending from the cylinder head to the crankcase. The upper ends of the upper oil drop hole half 58 open between the side edge portions 41a, 41b of the upper deck portion 41 and the water jacket wall 42. As shown in FIGS. 7 and 10 , the lower ends of the upper oil drop hole half 58 open in an elongated shape along the cylinder row direction, on the same plane as the lower surfaces of the joining flange portion 43 and the water jacket wall 42. That is, the lower end surface of the oil drop hole forming portion 46 forms part of the outer member side joining surface 57, and the lower ends of the oil drop hole upper halves 58 open into this outer member side joining surface 57. Then, a welding rib 56 (oil drop hole welding rib 56c) similar to the one described above is formed on the outer member side joining surface 57 so as to surround the periphery of each oil drop hole upper half 58.

[0039] The front flange portion 44 has an upper end portion that is continuous with the front edge portion 41c of the upper deck portion 41, forming a flange surface 44a (see FIG. 6) with relatively high rigidity. Similarly, the rear flange portion 45 has an upper end portion that is continuous with the rear edge portion 41d of the upper deck portion 41, forming a flange surface 45a (see FIG. 7) with relatively high rigidity. The flange surfaces 44a, 45a are aligned along a plane that is perpendicular to the cylinder row direction.

[0040] The lower sidewall 47 extends downward in the cylinder axial direction from a position on the outer periphery of the outer member joint surface 57 so as to cover the periphery of the base portion 12 on the main block 2 side. The lower end of the lower sidewall 47 is configured to reach near the upper surface of the upper deck portion 41 when combined with the main block 2. Furthermore, the lower sidewall 47 is cut out at the oil drop hole forming portion 46 to avoid interference with the oil drop hole forming portion 31 on the main block 2 side.

[0041] A cooling water inlet 59 (see FIG. 6) extending from the outer surface of the outer member 3 to the water jacket is provided on the eighth cylinder opposing surface 51H on the side of the #1 cylinder.

[0042] Next, the joining of the main block 2 and the outer member 3 and the composite cylinder block 1 finally constructed by this joining will be described.

[0043] As described above, the metal main block 2 and the synthetic resin outer member 3 are manufactured separately and then joined using a heat welding technique (a type of hot plate welding). The joining is performed between the top surface 22 of the base 12 and the outer member joining surface 57. In the joining process, a heater is disposed on the underside of the lower deck 11 of the metal main block 2, and the base 12 is heated from below while the main block 2 and the outer member 3 are separated. The heater is, for example, a plate-like configuration with four rectangular openings through which the main bearings 15 pass. The heater is provided in an area that covers at least the projected surface of the base 12 and is disposed so as to be in substantial contact with the underside of the lower deck 11. When the temperature near the top surface 22 of the base portion 12, which serves as the joining surface on the main block 2 side, rises to an appropriate temperature (e.g., about 200 to 300°C) at which the welding rib 56 of the synthetic resin outer member 3 can melt and soften, the outer member joining surface 57 is brought into close contact with the top surface 22 of the base portion 12, and the outer member 3 is pressed toward the main block 2. This melts the welding rib 56, joining the main block 2 and the outer member 3 together. Therefore, the welding rib 56 essentially serves as a seal line between them. If necessary, the top surface 22 of the base portion 12, which serves as the joining surface, may be treated with a suitable primer in advance to enhance the joining strength.

[0044] When they are joined together, a water jacket, which serves as a cooling water flow path, is formed between the cylinder wall 13 of the main block 2 and the water jacket-forming wall 42 of the outer member 3. This water jacket is sealed by the joint between the top surface 22 of the base portion 12, which is provided to surround the periphery of the cylinder wall 13, and the outer member-side joint surface 57. In other words, the water jacket is sealed at the welding rib 56, which serves as the seal line shown in FIG. 10 . Note that when the welding rib 56 is welded, the upper end surface of the cylinder wall 13 of the main block 2 and the upper surface of the upper deck portion 41 of the outer member 3 are aligned on approximately the same plane. Note that, considering that a rubber seal is used to form the seal between the upper deck portion 41 of the outer member 3 and the cylinder head, the upper surface of the upper deck portion 41 may be slightly lower than the upper end surface of the cylinder wall 13 of the main block 2.

[0045] All of the other seven columnar portions 14 except for the second columnar portion 14B are located inside the water jacket, and cooling water surrounds the outer circumferential surfaces of the columnar portions 14. A seal line consisting of the welding rib 56 passes outside the seven columnar portions 14, that is, outside the opening 54 (on the water jacket constituent wall 42 side), and seals the water jacket in a manner that includes the seven columnar portions 14. Therefore, as shown in FIG. 11 , for example, a relatively narrow water jacket exists between the outer circumferential surfaces of the columnar portions 14 and the water jacket constituent wall 42 (columnar portion opposing surface 52).

[0046] In contrast, the second columnar section 14B is housed in the second columnar section insertion hole 53 of the outer member 3 and is isolated from the water jacket. In other words, the second columnar section 14B is surrounded by a wall around the second columnar section insertion hole 53 made of synthetic resin and does not come into contact with the coolant. A small gap that serves as an air layer exists between the inner wall surface of the second columnar section insertion hole 53 and the outer peripheral surface of the second columnar section 14B.

[0047] The cylinder head (not shown) is placed on the upper surface of the upper deck portion 41 and fixed in place via cylinder head bolts. The cylinder head bolts are threaded into the bolt holes 24 of the columnar portions 14. The columnar portions 14, which serve as bolt bosses, each continue in a straight line along the cylinder axial direction all the way to the base portion 12, linearly transmitting the load along the bolt axial direction to the base portion 12. The base portion 12 is thick and sturdy, and reliably supports the load acting from the cylinder head. Similarly, the main bearing portion 15 is integrated with the sturdy base portion 12, enabling it to reliably support the crankshaft.

[0048] 1 and 11, the oil drop hole forming portion 31 of the main block 2 and the oil drop hole forming portion 46 of the outer member 3 are joined in a butt-together manner. As with the water jacket, the welding rib 56 (56c) provided on the outer member 3 melts and softens, and is joined to the joining surface (top surface 22) on the main block 2 side. As a result, the oil drop hole lower half 32 and the oil drop hole upper half 58 are connected as a single passage, thereby forming the oil drop hole. The upper end of the oil drop hole is further connected to the oil drop hole on the cylinder head side.

[0049] In this way, the composite cylinder block 1 of the above embodiment is configured so that the metal main block 2 that receives the load and reaction force has a minimum volume, and many parts such as the water jacket component wall 42 are made of synthetic resin as the outer member 3, thereby achieving a significant weight reduction.

[0050] Next, the main components of the present invention will be described. The composite cylinder block 1 is constructed by separately manufacturing the metal main block 2 and the synthetic resin outer member 3, and then joining them together by heat welding, such as hot plate welding. This simplifies the manufacturing process and allows for low-cost production. During heat welding, the metal main block 2, made of, for example, an aluminum alloy, is heated to, for example, approximately 200°C to 300°C. This causes thermal expansion in the cylinder row direction, potentially resulting in interference between the multiple columnar portions 14 and the synthetic resin outer member 3. Therefore, in the above embodiment, the dimension along the cylinder row of the minute gap between the outer surface of the columnar portion 14 facing outward in the cylinder row direction and the corresponding columnar portion-facing surface is set larger for columnar portions that are farther away from the center of the cylinder row in the cylinder row.

[0051] 12 is an enlarged plan view of a main portion of a composite cylinder block 1 formed by integrating a main block 2 and an outer member 3, and is an explanatory diagram that particularly enlarges and compares the vicinity of each of the columnar portions 14, namely, the first columnar portion 14A, the third columnar portion 14C, the fifth columnar portion 14E, and the seventh columnar portion 14G, which are aligned in the cylinder row direction. The center of the cylinder block 1 in the cylinder row direction is located between the third columnar portion 14C and the fifth columnar portion 14E.

[0052] Therefore, a gap Δ1 exists in the cylinder alignment direction between the outer surface of the first columnar portion 14A facing outward in the cylinder alignment direction and the corresponding columnar-portion-facing surface (the right-hand portion of the first columnar-portion-facing surface 52A in the figure), and a gap Δ3 exists in the cylinder alignment direction between the outer surface of the third columnar portion 14C facing outward in the cylinder alignment direction and the corresponding columnar-portion-facing surface (the right-hand portion of the third columnar-portion-facing surface 52C in the figure). Here, the relationship between the two is "Δ1 > Δ3." In other words, the dimension along the cylinder alignment of the minute gap between the outer surface of the columnar portion 14 facing outward in the cylinder alignment direction and the corresponding columnar-portion-facing surface is set to be larger for columnar portions that are farther away from the center in the cylinder alignment direction.

[0053] Similarly, a gap Δ6 exists in the cylinder alignment direction between the outer surface of the fifth columnar section 14E facing outward in the cylinder alignment direction and the corresponding columnar-section-opposing surface (the left-hand portion of the fifth columnar-section-opposing surface 52E in the figure), and a gap Δ8 exists in the cylinder alignment direction between the outer surface of the seventh columnar section 14G facing outward in the cylinder alignment direction and the corresponding columnar-section-opposing surface (the left-hand portion of the seventh columnar-section-opposing surface 52G in the figure).These gaps have a relationship of "Δ8 > Δ6."

[0054] In this configuration, even if the metal main block 2 is heated to, for example, about 200°C to 300°C during heat welding, and thermal expansion occurs along the cylinder row direction of the main block 2, interference does not occur between each columnar portion 14 and the corresponding columnar portion-facing surface. Therefore, heat welding can be achieved by heating the metal main block 2 to a temperature close to the melting temperature of the synthetic resin material. For example, during heat welding, the main block 2 and outer member 3 are each held by a jig and assembled based on the center in the cylinder row direction.

[0055] In the above embodiment, the entire joint surface, i.e., the welding surface, between the main block 2 and the outer member 3 is along a single plane perpendicular to the cylinder axial direction, which easily allows thermal expansion and contraction of the main block 2 along the cylinder row direction.

[0056] In the illustrated example, the third columnar portion 14C, the fifth columnar portion 14E, and the seventh columnar portion 14G are cylindrical with circular cross sections. The columnar portion-opposing surfaces 52C, 52E, and 52G that mate with these portions form arcuate surfaces with diameters larger than the diameters of the columnar portions 14C, 14E, and 14G by a predetermined amount. The centers of these arcuate surfaces (52C, 52E, and 52G) are offset from the centers of the columnar portions 14C, 14E, and 14G toward the outside in the cylinder alignment direction. Therefore, for example, a gap Δ7 is formed on the inside (right side of the figure) of the seventh columnar portion 14G in the cylinder alignment direction, but this gap Δ7 is smaller than the gap Δ8 on the outside in the cylinder alignment direction. In other words, Δ8 > Δ7. Similarly, due to the above-mentioned eccentricity, the third columnar portion 14C has a relationship of Δ3 > Δ4, and the fifth columnar portion 14E has a relationship of Δ6 > Δ5.

[0057] The first columnar portion opposing surface 52A is basically the same as the "8"-shaped first columnar portion 14A, and has a shape like two connected arcs of different diameters, each of which has a predetermined larger diameter than the diameters of the main cylindrical portion 14Aa and the sub-cylindrical portion 14Ab of the first columnar portion 14A, and the center of each arc is eccentric to the outer side in the direction of cylinder alignment (the right side in the figure). Therefore, for the first columnar portion 14A, a gap Δ2 occurring on the inner side in the direction of cylinder alignment (the left side in the figure) is smaller than the gap Δ1 on the outer side in the direction of cylinder alignment, so that "Δ1 > Δ2."

[0058] In this way, in the illustrated example, the columnar portion-facing surface, which has a similar shape to the outer surface of the columnar portion 14, is displaced (in other words, eccentric) outward in the cylinder row direction, and the amount of displacement (eccentricity) is set to be larger for columnar portions that are farther away from the center in the cylinder row direction. For example, the amount of eccentricity of the seventh columnar portion-facing surface 52G of the seventh columnar portion 14G is set to be larger than the amount of eccentricity of the fifth columnar portion-facing surface 52E of the fifth columnar portion 14E.

[0059] In this way, by configuring the basic shape of the columnar portion opposing surface to be similar to that of the columnar portion 14 and displaced in the cylinder row direction, the thickness of the synthetic resin outer member 3 near the columnar portion opposing surface does not become unnecessarily thin, which is advantageous in ensuring the rigidity and strength of the outer member 3.

[0060] The above-described gap dimension relationship and eccentricity outward in the cylinder row direction also apply to the openings 54 corresponding to the columnar portions 14 in the joining flange portion 43 shown in Figures 9 and 10. In other words, the inner circumferential surface of the openings 54 can be considered to be part of the surface facing the columnar portions.

[0061] Although not shown, the above-described gap dimensions in the cylinder row are identical to those for the second columnar section 14B, fourth columnar section 14D, sixth columnar section 14F, and eighth columnar section 14H, which are aligned in the cylinder row direction as shown in Fig. 2. The fourth columnar section 14D, sixth columnar section 14F, and eighth columnar section 14H are cylindrical with circular cross sections, and the columnar section-opposing surfaces 52D, 52F, and 52H that mate with these sections form arcuate surfaces with diameters that are larger than the diameters of the columnar sections 14D, 14F, and 14H by a predetermined amount. The centers of these arcuate surfaces (52D, 52F, and 52H) are eccentric outward in the cylinder row direction from the centers of the columnar sections 14D, 14F, and 14H, respectively.

[0062] As described above, the "8"-shaped second columnar portion 14B is provided with a second columnar portion insertion hole 53 that opens into the upper deck portion 41, and the inner circumferential surface of this second columnar portion insertion hole 53 serves as the columnar portion-facing surface. The second columnar portion insertion hole 53 has a shape like two arcs connected together, each with a different diameter. Each arc has a diameter that is larger than the diameters of the main columnar portion 14Ba and the sub-columnar portion 14Bb of the second columnar portion 14B by a predetermined amount, and the center of each arc is eccentric to the outside in the cylinder row direction (to the right in FIG. 2). This is similar to the relationship between the first columnar portion 14A and the first columnar portion-facing surface 52A shown in FIG. 12.

[0063] Therefore, for each of the second columnar section 14B, fourth columnar section 14D, sixth columnar section 14F, and eighth columnar section 14H, there are gaps Δ1, Δ2, Δ3, Δ4, Δ5, Δ6, Δ7, and Δ8, and the relationships of "Δ1 > Δ3" and "Δ8 > Δ6" are established, as in Fig. 12. Furthermore, for each columnar section 14, the relationships of "Δ1 > Δ2," "Δ3 > Δ4," "Δ6 > Δ5," and "Δ8 > Δ7" are established due to the eccentricity of the arc centers described above.

[0064] The dimensional difference between the gaps and the eccentricity of the arc center will differ depending on the number of cylinders, cylinder diameter, material of the main block 2, etc., and are set optimally taking into consideration the temperature during heat welding, etc.

[0065] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the columnar portions 14 other than the second columnar portion 14B are located inside the water jacket, but all of the columnar portions 14 may be located outside the water jacket, like the second columnar portion 14B. Conversely, all of the columnar portions 14, including the second columnar portion 14B, may be located inside the water jacket. Furthermore, the columnar portions 14 may be shaped like a rectangular pillar or other shapes other than a cylindrical pillar. [Explanation of symbols]

[0066] 1...Composite cylinder block 2...Main block 3...Outer member 11...Lower deck 12...Base 13...Cylinder wall 14...Columnar part 15...Main bearing part 24...Bolt hole 52... Column facing surface 53...Second columnar part insertion hole 53 (column part opposing surface)

Claims

1. A composite cylinder block comprising: a metal main block including at least a cylinder wall and a main bearing portion; and an outer member made of synthetic resin configured to surround the cylinder wall, forming a water jacket between the metal main block and the cylinder wall, and including an upper deck portion on which a cylinder head is disposed, wherein the outer member is heat-welded to the main block by heating the main block, the main block includes a plurality of pillars that extend upright to reach an upper surface of the upper deck portion and correspond to cylinder head bolts that fix the cylinder head, the outer member has a columnar portion facing surface that faces an outer surface of the columnar portion via a small gap, In this composite cylinder block, the dimension along the cylinder row of the minute gap between the outer surface of each pillar portion facing outward in the cylinder row direction and the corresponding opposing surface of the pillar portion is set to be larger for pillar portions that are farther away from the center in the cylinder row direction.

2. The columnar portion has a cylindrical shape with a circular cross section, 2. The composite cylinder block according to claim 1, wherein the opposing surface of the columnar portion is an arcuate surface having a diameter larger than a diameter of the columnar portion by a predetermined amount.

3. 3. The composite cylinder block according to claim 2, wherein the center of said arcuate surface is eccentric from the center of said columnar portion toward the outside in the direction of cylinder alignment, at least in the columnar portion located at the end in the direction of cylinder alignment.

4. the columnar portion is located within the water jacket; 4. The composite cylinder block according to claim 1, wherein the columnar portion opposing surface is configured as a concave groove surface between two cylinder opposing surfaces that oppose the outer peripheral surface of the cylinder wall so as to form the water jacket.

5. The columnar portion is located independently from the water jacket, 4. The composite cylinder block according to claim 1, wherein the columnar portion facing surface is configured as a hole into which the columnar portion is inserted in the cylinder axial direction.

6. 6. The composite cylinder block according to claim 1, wherein the entire welded surfaces of said main block and said outer member lie on a single plane perpendicular to the cylinder axial direction.

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