Composite cylinder block

Abstract

A complexed cylinder block (1) for an internal combustion engine is formed from a metal main block (2) and a synthetic resin outer member (3). The main block (2) includes a lower deck (11), a base part (12), and cylinder walls (13). The outer member (3) includes an upper deck part (41), and a water-jacket forming walls (42) that surround the cylinder walls (13) and that forms a water jacket. Outer-member-side joint surfaces (57) at the lower end of the water-jacket forming walls (42) are provided with welding ribs (56), and are heat-welded to the top surface (22) of the base part (12) by applying, onto the main block (2), pressure and heat from the lower surface side by a heater. The welding surfaces of both sides are on the same plane orthogonal to the cylinder axis direction, and have a uniform temperature during welding. Accordingly, high welding quality is exhibited.

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 removing, by machining, the outer wall portion 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 onto the outer peripheral surface of the cylinder liner. The cylindrical wall of the resin block is bonded to the inner peripheral surface of the cylinder liner via an adhesive layer provided on the outer peripheral surface of the cylinder liner, thereby integrating the resin block and the metal block.

[0003] In the cylinder block of Patent Document 1, the metal cylinder liner does not come into direct contact with the cooling water, and the actual water jacket is formed inside the resin block. In other words, the water jacket is not formed between the metal cylinder liner and the resin block.

[0004] Patent Document 2 discloses a cylinder block including a metal cylinder block body and a synthetic resin outer wall that surrounds the cylinder liner of the metal cylinder block body to form a water jacket. A cylindrical metal insert is embedded in the synthetic resin outer wall, and the cylinder head bolt and a long bearing cap bolt are screwed into the metal insert from above and below, respectively, so that the synthetic resin outer wall is sandwiched between the cylinder head and the cylinder block body.

[0005] In this configuration, the weight of the synthetic resin member is increased by the metal insert, and the weight of the entire cylinder block is increased because two metal bolts are disposed across the entire height of the cylinder block, which significantly reduces the weight reduction effect achieved by using a part of the cylinder block as a synthetic resin member. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-112147 A [Patent Document 2] JP 2005-146880 A Summary of the Invention

[0007] 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 and to form a water jacket between the metal main block and the cylinder wall, the outer member being heat-welded to the main block by heating the main block, The entire welded surfaces of the main block and the outer member are on a single plane perpendicular to the cylinder axial direction.

[0008] In other words, in the composite cylinder block of this invention, the synthetic resin outer member and the metal main block are heat-welded with slight melting of the contact surface of the synthetic resin outer member. In this invention, the entire welding surface is on a plane perpendicular to the cylinder axial direction, so that each part of the welding surface can be kept at a uniform temperature during welding, resulting in uniform welding quality in each part.

[0009] Therefore, the synthetic resin outer member does not include metal inserts or the like, and the weight of the entire cylinder block can be significantly reduced. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a perspective view of a composite cylinder block according to an embodiment of the present invention; [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 4 is a perspective view of the outer member in a upside-down state. [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 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will now be described in detail with reference to the drawings.

[0012] First, the overall structure of a composite cylinder block 1 of one embodiment will be described. The composite cylinder block 1 is composed of two members: a metal main block 2 and an outer member 3 made of synthetic resin. 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 the outer member 3 are manufactured separately and welded together using a heat welding technique described below.

[0013] The illustrated example is a cylinder block 1 for an in-line three-cylinder engine, and for convenience of explanation, as indicated by "#1" in FIG. 1, the cylinders will be called #1, #2, and #3, starting from the right front side of FIG. 1. The direction parallel to the line on which the centers of these three cylinders are aligned will be called the "cylinder row direction", the direction parallel to the central axis of each cylinder will be called the "cylinder axis direction", and the direction perpendicular to the cylinder row direction will be called the "width direction". In addition, following the general directions of top dead center and bottom dead center, the terms "upper", "upper", "lower", and "lower" will be used. Note that the present invention is not limited to an in-line three-cylinder engine. Furthermore, the "front" of the cylinder block 1 means the #1 cylinder side in the cylinder row direction, and the "rear" means the #3 cylinder side.

[0014] The metallic main block 2 is an integral assembly of parts that support the load or reaction force caused by the combustion and explosion of the internal combustion engine, and each part is cast integrally using an appropriate metallic material. In a preferred embodiment, it is cast integrally by die casting using an aluminum alloy. As shown in Figs. 4 and 5, the main block 2 includes a lower deck 11 having a plate shape along a plane perpendicular to the cylinder axis direction, a base portion 12 rising upward from the upper surface of the lower deck 11, three cylindrical cylinder walls 13 extending further upward from the base portion 12, a total of eight columnar portions 14 also rising upward from the base portion 12, and four main bearing portions 15 provided on the lower surface of the lower deck 11. Each cylinder wall 13 forms a cylinder bore 16, and these cylinder bores 16 extend through the base portion 12 to the lower surface of the lower deck 11.

[0015] The lower deck 11 expands in a generally symmetrical manner 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-like lower deck 11 has an appropriate thickness to provide the necessary rigidity. The cylinder bores 16 terminate at the lower surface of the lower deck 11. In other words, the cylinder wall 13 does not protrude downward beyond the lower deck 11. When the engine is finally assembled, a crankcase component (e.g., an oil pan) (not shown) is attached to the lower surface of the lower deck 11.

[0016] The main bearings 15 are provided at four locations, including the front and rear ends in the cylinder row direction and between the cylinders, in order to rotatably support the crankshaft (not shown). Each of the main bearings 15 is formed as a relatively thick rectangular plate that protrudes downward from the lower surface of the lower deck 11, and has a semicircular bearing recess 15a at the center of the lower surface. Bearing caps (not shown) are finally attached to these main bearings 15, and the journal portion of the crankshaft is rotatably supported via a bearing metal (not shown). The lower surface of the lower deck 11, except for the main bearings 15, is a flat surface along a plane perpendicular to the cylinder axial direction.

[0017] The cylinder wall 13 has a cylindrical shape with 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 or a wear-resistant metal is sprayed on the inner peripheral surface of the cylinder bore 16.

[0018] The base portion 12 has a side surface 21 rising substantially at a right angle from the upper surface of the lower deck 11, and a top surface 22 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 substantially at a right angle (in other words, along the cylinder axial direction).

[0019] The pillar-shaped portions 14 are provided at eight locations in total, including both front and rear ends in the cylinder row direction and between the cylinders, so as to surround the cylinder row in which the three cylinder walls 13 are connected. In the following, when it is necessary to distinguish between them, they are called 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, in order from the #1 cylinder side, as shown in FIG. 4, and when it is not necessary to distinguish between them, they are collectively called the pillar-shaped portion 14. Each pillar-shaped portion 14 is independent and is also separated from the cylinder wall 13. These pillar-shaped portions 14 function as bolt boss portions into which cylinder head bolts (not shown) for fixing a cylinder head (not shown) arranged on the cylinder block 1 are screwed.

[0020] The six columnar sections 14 excluding the first columnar section 14A and the second columnar section 14B, that is, 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 screwed is formed at the center of the upper end. Basically, the diameters of the third columnar section 14C to the eighth columnar section 14H are set to be equal to each other. Here, in the illustrated example, since the main block 2 is cast by a die casting method, a so-called draft is given to the surface of each section along the cylinder axial direction as necessary, and 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.

[0021] Unlike the third columnar portion 14C to the eighth columnar portion 14H, the first columnar portion 14A has a shape as if two parallel cylinders were joined at a part of the outer circumferential surface. In other words, in a plan view as shown in FIG. 5 and a cross-sectional view perpendicular to the cylinder axis direction, the first columnar portion 14A has a shape of the letter "8". Specifically, a main columnar portion 14Aa having a diameter similar to that of the third columnar portion 14C to the eighth columnar portion 14H and a sub-columnar portion 14Ab having a smaller diameter are integrated. The main columnar portion 14Aa is a portion that functions as a bolt boss portion for a cylinder head bolt like the third columnar portion 14C to the eighth columnar portion 14H, and has a bolt hole 24 at the center of the upper end portion. This main columnar portion 14Aa is provided at a position symmetrical to the fourth columnar portion 14D across the center of the #1 cylinder, that is, at a position where a total of eight cylinder head bolts are evenly arranged. The sub-cylindrical portion 14Ab is located diagonally outside the main cylindrical portion 14Aa, that is, on the opposite side to the cylinder wall 13 of the #1 cylinder. An oil passage 25 is formed in the center of the 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 tube constituting the oil passage 25 having 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 tube of the oil passage 25, at part of the circumferential surface, and a pair of recessed grooves 14Ac remain on the outer circumferential surface between them.

[0022] The second columnar portion 14B is similar to the first columnar portion 14A and has a shape as if two parallel cylinders were joined at a part of the outer circumferential surface. In other words, in the plan view and the cross-sectional view perpendicular to the cylinder axis direction as shown in FIG. 5, it has a shape of the letter "8". Specifically, the main columnar portion 14Ba, which has a smaller diameter than the third columnar portion 14C to the eighth columnar portion 14H, and the sub-columnar portion 14Bb, which has a slightly smaller diameter than the main columnar portion 14Ba, are integrated together. The main columnar portion 14Ba is a portion that functions as a bolt boss portion for the cylinder head bolts, similar to the third columnar portion 14C to the eighth columnar portion 14H, and has a bolt hole 24 at the center of the upper end portion. This main columnar portion 14Ba is provided at a position symmetrical to the third columnar portion 14C across the center of the #1 cylinder, that is, at a position where the arrangement of the total eight cylinder head bolts is uniform. The sub-cylindrical portion 14Bb is located in front of and inward of the main cylindrical portion 14Ba in the width direction, that is, next to the main cylindrical portion 14Ba on an arc centered on the center of the cylinder #1. In the center of this sub-cylindrical portion 14Bb, an oil passage 26 is formed along the cylinder axial direction to supply oil pressurized by an oil pump (not shown) to the cylinder head, similar to the sub-cylindrical portion 14Ab of the first columnar portion 14A. In other words, the sub-cylindrical portion 14Bb corresponds to a tube constituting the oil passage 26 having a circular cross section. In this way, the second columnar portion 14B is formed by connecting the main cylindrical portion 14Ba, which is the bolt boss portion, and the sub-cylindrical portion 14Bb, which is the tube of the oil passage 26, at a part of the circumferential surface, and a pair of recessed grooves 14Bc remain on the outer circumferential surface between them.

[0023] In the illustrated example, the second columnar section 14B is configured such that its lower portion 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 circumferential surface of the second columnar section 14B having an "8"-shaped cross section, its inner portion (portion toward the cylinder wall 13) rises up from the top surface 22 of the base section 12, whereas its outer portion (portion opposite the cylinder wall 13) extends below the top surface 22 and continues to the lower deck 11.

[0024] 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 are each connected to a sub-oil gallery (not shown) extending in the width direction of the main block 2 formed near the front end of the lower deck 11. The sub-oil gallery along the width direction is connected to a main oil gallery 27 (see Figs. 11 and 4) extending along the cylinder row direction 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 part of this high-pressure oil is supplied to the cylinder head side through two oil passages 25 and 26. Also, as shown in Fig. 11, a part of the high-pressure oil is supplied to the bearing recess 15a through an oil passage 28 passing through the main bearing portion 15.

[0025] 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 thereof. Basically, 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.

[0026] In other words, as shown in Fig. 5, the top surface 22 exists with a substantially constant width (see reference 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 reference 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 around the other columnar portions 14, following the "8"-shaped cross-sectional shape of the first columnar portion 14A. In addition, the top surface 22 exists with a relatively narrow width between each columnar portion 14 except the second columnar portion 14B and the adjacent cylinder wall 13.

[0027] As for the second columnar portion 14B, since both the main columnar portion 14Ba and the sub columnar portion 14Bb have smaller diameters than the other columnar portions 14, a top surface 22 having a width approximately equal to the width (see D1 in FIG. 5) of the portion other than the portion adjacent to the other columnar portion 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.

[0028] Furthermore, the base portion 12 has three oil drop hole forming portions 31 each having a rectangular shape in a plan view. The first oil drop hole forming portion 31A is located between the #1 cylinder and the #2 cylinder and is located outside the third columnar portion 14C, and the second oil drop hole forming portion 31B is located between the #2 cylinder and the #3 cylinder and is located 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 these two oil drop hole forming portions 31A and 31B, and is located between the fourth columnar portion 14D and the sixth columnar portion 14F, that is, on the side of the #2 cylinder. In the center of each of these oil drop hole forming portions 31, a lower half of the oil drop hole 32 extending in the cylinder axial direction is formed. As described later, the lower half of the oil drop hole 32 forms a part of the oil drop hole for returning oil used on the cylinder head side to the crankcase by its own weight. 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 FIG. 5, but on the underside of the lower deck 11, which is the final oil outlet, the shape is narrowed to a circular hole, as shown in FIG. 3.

[0029] 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 lower half of the oil drop hole 32.

[0030] The 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 aligned along a single plane perpendicular to the cylinder axial direction. As will be described later, this top surface 22 is the surface that becomes the joint surface with the synthetic resin outer member 3, and forms a plane perpendicular to the cylinder axial direction and therefore is a plane parallel to the lower surface of the lower deck 11.

[0031] Next, the synthetic resin outer member 3 is not a member that supports the load or reaction force accompanying the combustion and explosion of the internal combustion engine, but mainly constitutes a water jacket through which cooling water flows between the main block 2 and the upper deck portion that serves as the joint surface with the cylinder head, and each part is integrally formed 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 a polyamide resin.

[0032] As shown in Fig. 6 to Fig. 10, the outer member 3 is generally in the shape of a rectangular frame or cylinder. The main parts of the outer member 3 include an upper deck portion 41 which is a joint or boundary surface with the cylinder head, a water jacket wall 42 which surrounds the cylinder wall 13 of the main block 2 and the columnar portion 14 other than the second columnar portion 14B to form a water jacket, a joint flange portion 43 which protrudes from the lower end of the water jacket wall 42 to the inner periphery, a front flange portion 44 and a rear flange portion 45 which are the front end face and the rear end face of the composite cylinder block 1, an oil drop hole forming portion 46 which respectively correspond to the oil drop hole forming portion 31 on the main block 2 side, and a lower side wall portion 47 which covers the periphery of the base portion 12 on the main block 2 side. As described later, the outer member 3 is combined with the main block 2 so as to cover the main block 2 while accommodating the cylinder wall 13 of the main block 2 on the inner periphery side of the water jacket wall 42.

[0033] The upper deck portion 41 is connected to the upper end of the outer member 3 in a substantially rectangular frame shape, and its upper surface is a flat surface along a plane perpendicular to the cylinder axial direction. The upper deck portion 41 includes left and right side edges 41a, 41b that are linear, a front edge 41c, and a rear edge 41d. The side edges 41a, 41b are connected to the upper part of the water jacket component wall 42 located on the inside via several ribs 41e that extend in the width direction. The upper end surface of the water jacket component wall 42 constitutes a part of the upper deck portion 41, and is along a single plane together with the side edges 41a, 41b, the front edge 41c, and the rear edge 41d. The cylinder head (not shown) is mounted on the upper deck portion 41 via a cylinder head gasket (not shown). As a cylinder head gasket, for example, a composite gasket is used in which the portion in contact with the metal main block 2, such as the top surface of the cylinder wall 13, is a metal seal, and the portion in contact with the synthetic resin upper deck portion 41 is a rubber seal.

[0034] The water jacket constituent wall 42 has a shape that generally follows the outer contour of the cylinder wall 13 and the columnar portion 14 (excluding the second columnar portion 14B) of the main block 2 in a plan view, and has a wall surface that is substantially parallel to the cylinder axis direction. More specifically, the water jacket constituent wall 42 is configured by combining a total of eight cylinder facing surfaces 51, three on each side of the left and right and three on the front and rear ends, which are relatively gently curved and face the outer circumferential surface of the cylinder wall 13 without overlapping with the columnar portion 14, and a total of seven columnar portion facing surfaces 52 that surround the columnar portion 14 other than the second columnar portion 14B. As shown in FIG. 9, when it is necessary to distinguish the eight cylinder facing surfaces 51 individually, they are called the first cylinder facing surface 51A, the second cylinder facing surface 51B, to the eighth cylinder facing surface 51H in the clockwise direction 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,..., 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.

[0035] 1, the position of the cylinder facing surface 51 is set so that an appropriate gap (in other words, a water jacket) of, for example, about several millimeters is formed between the cylinder wall 13 and the cylinder facing surface 51 when the cylinder facing surface 51 is combined with the main block 2. In contrast, the columnar portion facing surface 52 is configured to be an arc 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 14 and the outer circumferential surface of each columnar portion 14, and to be generally concentric with each columnar portion 14 when the cylinder facing surface 51 is combined with the main block 2. More specifically, the third columnar portion facing surface 52C to the sixth columnar portion 14F 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 portion facing surface 52G and the eighth columnar portion facing surface 52H corresponding to the seventh columnar portion 14G and the eighth columnar portion 14H are located at positions corresponding to the corners of the ends of the continuous water jacket, and therefore form cylindrical surfaces with a cross section of about 3 / 4 of a circle, which is larger than a semicircle. In other words, about 3 / 4 of the circumference of the seventh columnar portion 14G and the eighth columnar portion facing surface 52H is surrounded by the seventh columnar portion facing surface 52G and the eighth columnar portion facing surface 52H. The first columnar portion facing surface 52A corresponding to the first columnar portion 14A has a cross section that follows the outline of the character "8" so that a small gap remains all around, corresponding to the first columnar portion 14A that has a cross section shaped like the character "8". As a result, as shown in FIG. 1, the first columnar portion 14A fits into the first columnar portion facing surface 52A with a small gap remaining all around.

[0036] The second columnar portion 14B does not have a corresponding groove (columnar portion facing surface) in the water jacket component wall 42. The second columnar portion insertion hole 53 is formed in a pipe shape extending in the cylinder axial direction on the outside of the water jacket component wall 42 (specifically, the first cylinder facing surface 51A to the eighth cylinder facing surface 51H) so as to be independent of 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 having an "8"-shaped cross section. The second columnar portion insertion hole 53 having a cross-sectional shape that follows the outline of the figure "8" opens at the upper end on the upper 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 with a slight gap remaining all around.

[0037] The joint flange portion 43, which protrudes from the lower end of the water jacket wall 42 toward the inner periphery, is formed along a plane perpendicular to the cylinder axial direction together with the lower end surface of the water jacket wall 42, and constitutes the outer member side joint surface 57. This outer member side joint surface 57 is basically shaped to correspond to the area of ​​the top surface 22 of the base portion 12 of the main block 2. That is, the joint flange portion 43 protrudes like an eave so as to follow the contour of the periphery of the three cylinder walls 13 connected in series on the top surface 22 of the base portion 12, and has seven openings 54 corresponding to the seven columnar portions 14 except the second columnar portion 14B, and the outer member side joint surface 57 is continuously formed 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 approximately shaped like the letter "8" similar to the first columnar portion facing surface 52A. The outer opening edge of each opening 54 is continuous with the corresponding columnar portion facing surface 52 in the cylinder axial direction without any step.

[0038] 7, 8 and 10, a welding rib 56 is formed on the outer member side joining surface 57, including the lower surface of the water jacket constituent wall 42 and the lower surface of the joining flange portion 43, so as to heat-weld the synthetic resin material and protrude downward in a bead shape of a certain width from the outer member side joining surface 57. The welding rib 56 has a main welding rib 56a that is continuous around the entire circumference so as to pass around the outsides of the three cylinder walls 13 and the seven columnar portions 14, similar to the contour of the water jacket constituent wall 42, and a columnar portion welding rib 56b that is in the shape of an arc and that individually fits the inside portions (portions that enter between the cylinders) of the seven openings 54, and the columnar portion welding rib 56b is continuous with the main welding rib 56a.

[0039] 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) until only a small portion remains.

[0040] The oil drop hole forming portion 46 of the outer member 3 is provided at three locations on the outer member 3 so as to correspond to the oil drop hole forming portion 31 on the main block 2 side. Each oil drop hole forming portion 46 protrudes downward from the upper deck portion 41 in a duct shape, and an oil drop hole upper half portion 58 extending in the cylinder axial direction is formed on the inner peripheral side. This oil drop hole upper half portion 58 is continuous with the oil drop hole lower half portion 32 on the main block 2 side to form an oil drop hole extending from the cylinder head to the crankcase. The upper end of the oil drop hole upper half portion 58 opens between the side edge portions 41a, 41b of the upper deck portion 41 and the water jacket component wall 42. The lower end of the oil drop hole upper half portion 58 opens in an elongated shape along the cylinder row direction on the same plane as the joint flange portion 43 and the lower surface of the water jacket component wall 42, as shown in Figures 7 and 10. In other words, the lower end surface of the oil drop hole forming portion 46 forms part of the outer member side joint surface 57, and the lower ends of the oil drop hole upper halves 58 open into this outer member side joint surface 57. Also, a welding rib 56 (welding rib 56c for oil drop hole) similar to that described above is formed on the outer member side joint surface 57 so as to surround the periphery of each oil drop hole upper halves 58.

[0041] The front flange portion 44 has an upper end portion continuous with the front end edge portion 41c of the upper deck portion 41, and forms a flange surface 44a (see FIG. 6) having relatively high rigidity. Similarly, the rear flange portion 45 has an upper end portion continuous with the rear end edge portion 41d of the upper deck portion 41, and forms a flange surface 45a (see FIG. 7) having relatively high rigidity. The flange surfaces 44a, 45a are aligned along a plane perpendicular to the cylinder row direction.

[0042] The lower sidewall portion 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 portion 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 portion 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.

[0043] 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.

[0044] 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.

[0045] As described above, the metallic 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 side joining surface 57. In the joining process, a heater is disposed on the underside of the lower deck 11 of the metallic main block 2, and the base 12 is heated from below while the main block 2 and the outer member 3 are separated from each other. The heater is, for example, in a plate-like configuration with four rectangular openings through which the main bearings 15 pass, and is provided in an area that covers at least the projection surface of the base 12 and is disposed so as to be substantially in close contact with the underside of the lower deck 11. When the temperature near the top surface 22 of the base portion 12, which is the joint surface on the main block 2 side, rises to an appropriate temperature (for example, 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 side joint 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, and the main block 2 and the outer member 3 are joined together. Therefore, the welding rib 56 essentially becomes a seal line between them. In order to increase the joining strength, an appropriate primer treatment may be applied in advance to the top surface 22 of the base portion 12, which is the joint surface, as necessary.

[0046] When they are joined together, a water jacket serving as a flow path for cooling water 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 joining between the top surface 22 of the base portion 12 provided so as to surround the periphery of the cylinder wall 13 and the joining surface 57 of the outer member side. That is, the water jacket is sealed at the welding rib 56 serving 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 the seal between the upper deck portion 41 of the outer member 3 and the cylinder head is a rubber seal, 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.

[0047] All of the other seven columnar portions 14 except for the second columnar portion 14B are 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 including 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).

[0048] 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 cooling water. 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.

[0049] The cylinder head (not shown) is placed on the upper surface of the upper deck portion 41 and fixed via cylinder head bolts. The cylinder head bolts are screwed 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 up to the base portion 12, and linearly transmit the load along the bolt axial direction to the base portion 12. The base portion 12 is thick and solidly constructed, and reliably supports the load acting from the cylinder head. Similarly, the main bearing portion 15 is integrated with the solid base portion 12, and can reliably support the crankshaft.

[0050] As shown in Fig. 1 and Fig. 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 by butting against each other. 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, 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.

[0051] In this manner, the composite cylinder block 1 of the above embodiment is constructed 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.

[0052] Next, the main part of the present invention will be described. In the above-mentioned composite cylinder block 1, the metal main block 2 and the synthetic resin outer member 3 are manufactured separately and are integrally joined by heat welding such as a kind of hot plate welding, so that the manufacturing process is simple and the manufacturing cost can be reduced. As described above, in the above-mentioned embodiment, the top surface 22 of the base portion 12 of the metal main block 2 and the outer member side joining surface 57 of the synthetic resin outer member 3 are joined to each other to form a welding surface. This welding surface (top surface 22 and outer member side joining surface 57) is on a single plane that surrounds the entire circumference of the water jacket and is perpendicular to the cylinder axial direction. Therefore, when the lower surface side of the lower deck 11 is heated by the above-mentioned heater from the underside in the welding process, the temperature of the top surface 22, which is one of the welding surfaces, becomes uniform at each part, and as a result, uniform welding quality is obtained at each part in the circumferential direction surrounding the water jacket. In other words, good sealing performance is obtained for the entire water jacket.

[0053] In particular, in the illustrated example, the underside of the lower deck 11 (i.e., the heated surface) with which the heater comes into contact also lies along a plane perpendicular to the cylinder axial direction, and the distance (length along the cylinder axial direction) from the heated surface that receives heat to the top surface 22, which is the welding surface, is constant at each portion. Therefore, a uniform temperature distribution is achieved at the top surface 22. As described above, the area of ​​the underside of the lower deck 11 excluding the main bearing portion 15 (for example, a rectangular area obtained by projecting the outer shape of the upper deck portion 41 of the outer member 3 in the cylinder axial direction) becomes the heated surface that comes into contact with the heater.

[0054] During heat welding, the outer member 3 is pressed toward the main block 2 with a predetermined load, and the welding rib 56 is pressed against the top surface 22. However, since the welding surface (top surface 22 and outer member side joint surface 57) is a plane perpendicular to the cylinder axial direction, no unnecessary component force is generated during the application of pressure, and pressure can be applied reliably at each part.

[0055] During operation of the internal combustion engine, the continuous welding surface surrounding the water jacket (in other words, the welding ribs 56a, 56b) except for the oil drop hole welding rib 56c is in contact with the cooling water in the water jacket over its entire circumference. Therefore, the welding surface does not become excessively hot during operation, and each part can be maintained at a uniform temperature. This increases the durability of the welding, and the deterioration of the sealing performance is suppressed over a long period of time.

[0056] Furthermore, in the illustrated example, the top surface 22 of the base portion 12, which is the welding surface, is located at the midpoint of the axial dimension of the cylinder bore 16. Therefore, the water jacket is formed to surround only the upper half of the cylinder bore 16, which is subject to a high thermal load, which is advantageous in terms of accelerating warm-up.

[0057] Although one embodiment of the present invention has been described above in detail, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the columnar portion 14 except for the second columnar portion 14B is in the water jacket and the welding surface is set on the outside thereof, but the welding surface may be set so that the columnar portion 14 is on the outside of the water jacket. Even if the top surface 22, which is the welding surface, is heated from the outside (above) as in general hot plate welding during heat welding, the top surface 22 is aligned along a plane perpendicular to the cylinder axial direction, so that the heat capacity of each portion is uniform, which is advantageous in terms of uniform temperature distribution.

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 and to form a water jacket between the metal main block and the cylinder wall, the outer member being heat-welded to the main block by heating the main block, the main block includes a plate-like lower deck in which the lower ends of the cylinder bores are open to a lower surface and the main bearing portions are formed so as to protrude downward, a base portion formed on an upper surface of the lower deck, and the cylinder wall rising from a top surface of the base portion, the lower deck is formed in a plate shape along a plane perpendicular to the cylinder axial direction, and a lower surface thereof constitutes a heated surface that receives heat during heat welding; an entire welded surface between the main block and the outer member is on a single plane perpendicular to a cylinder axial direction; the main block side joining surface and the outer member side joining surface constituting the welding surface are each flat, and the top surface of the base portion surrounding the cylinder wall constitutes the main block side joining surface, A continuous bead-shaped welding rib is formed on the outer member side joining surface around the entire circumference surrounding the plurality of cylinder walls, and the main block and the outer member are welded to each other with the welding rib melted. Composite cylinder block.

2. 2. The composite cylinder block according to claim 1, wherein the welded surface is continuous and surrounds the periphery of the water jacket, and the welded portion is in contact with the cooling water over the entire periphery.

3. (delete)

4. 3. The composite cylinder block according to claim 1, wherein the lower surface of said cylinder block excluding said main bearing portion constitutes said heated surface.

5. (delete)

6. 5. A composite cylinder block according to claim 1, wherein said main block is integrally formed by casting using a metallic material, and said outer member is integrally formed by injection molding using a synthetic resin material.

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