Composite cylinder block

Abstract

To decrease the weight of a compound type cylinder block 1 by providing a part of an oil falling hole on which hydraulic pressure does not act, in a synthetic resin outer member 3.SOLUTION: A compound type cylinder block 1 of an internal combustion engine, is composed of a metallic main block 2, and a synthetic resinous outer member 3, and is heat-welded on a joint surface orthogonal to a cylinder axis direction. The main block 2 includes a lower deck 11, a pedestal portion 12, and a cylinder wall 13. The outer member 3 includes an upper deck portion 41, and a water jacket structure wall 42. An oil falling hole upper half portion 58 is formed on the outer member 3 side, and an oil falling hole lower half portion 32 is formed on the main block 2 side.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] This invention relates to a composite cylinder block for an internal combustion engine composed of a combination of a metal member and a synthetic resin member.

Background Art

[0002] Patent Document 1 discloses a cylinder block including a metal cylinder block body and an outer wall made of synthetic resin that surrounds the cylinder liner of the metal cylinder block body to form a water jacket. A cylindrical metal insert is embedded in the outer wall made of synthetic resin, and a cylinder head bolt and a long bearing cap bolt are screwed into the metal insert from above and below, respectively, so that the outer wall made of synthetic resin is sandwiched between the cylinder head and the cylinder block body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, a cylinder head disposed on the upper surface of a cylinder block of an internal combustion engine includes a valve operating mechanism and the like, and oil supply is required for its lubrication and use as a hydraulic source. The oil used on the cylinder head side is recovered into the crankcase by its own weight through an oil drain hole provided vertically in the cylinder block.

[0005] In Patent Document 1 above, an oil drain hole is not described, and no consideration is given to how to configure the oil drain hole.

Means for Solving the Problems

[0006] The present invention relates to 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, form a water jacket between the cylinder wall, and having a cylinder head disposed on the upper surface, and an upper deck portion, and the two are integrally joined together. The upper half of the oil drain hole extending from the cylinder head to the crankcase below the main block is formed inside the synthetic resin material of the outer member, and the lower half is formed inside the metal material of the main block, and the periphery of the oil drain hole is surrounded by a joint surface.

[0007] Since the oil flowing through the oil drain hole has already been used in the cylinder head and has a reduced pressure, a high oil pressure does not act on the oil drain hole. That is, high pressure resistance is not required, and a part of the oil drain hole can be provided on the side of the synthetic resin outer member.

Advantages of the Invention

[0008] According to the present invention, since the upper half of the oil drain hole is formed inside the relatively lightweight outer member, the overall weight of the composite cylinder block can be reduced as compared with the case where the entire oil drain hole is formed inside a metal member.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] First, the overall configuration of the 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 a synthetic resin outer member 3. FIGS. 1 to 3 and FIG. 11 show the composite cylinder block 1 in a state where the main block 2 and the outer member 3 are integrated. FIGS. 4 and 5 show the main block 2 alone, and FIGS. 6 to 10 show the outer member 3 alone. The main block 2 and the outer member 3 are each manufactured individually and are welded together using a heat welding technique described later.

[0012] The illustrated example is a cylinder block 1 for an in-line three-cylinder engine. For the sake of convenience of explanation, as attached with "♯1" etc. in FIG. 1, from the front right side of FIG. 1 in order, it will be called the ♯1 cylinder, the ♯2 cylinder, and the ♯3 cylinder. And the direction parallel to the straight line on which the centers of these three cylinders are arranged 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 orthogonal to the cylinder row direction will be called the "width direction", respectively. Also, following the general top dead center and bottom dead center directions, terms such as "up", "above", "down", "below" are used. Note that the present invention is not limited to an in-line three-cylinder engine. Further, 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.

[0013] The metal main block 2 integrates in one body the parts that support the loads or reaction forces associated with the combustion and explosion of the internal combustion engine, and is integrally cast using an appropriate metal material for each part. In a preferred embodiment, it is integrally cast by die-casting using an aluminum alloy. As shown in FIGS. 4 and 5, the main block 2 includes a lower deck 11 in the form of a plate along a plane orthogonal to the cylinder axis direction, a pedestal portion 12 rising upward from the upper surface of the lower deck 11, three cylindrical cylinder walls 13 extending further upward from the pedestal portion 12, a total of eight columnar portions 14 rising upward from the pedestal portion 12 as well, 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 penetrate the pedestal portion 12 and extend to the lower surface of the lower deck 11.

[0014] The lower deck 11 spreads out so as to be substantially symmetric in the width direction around the cylinder bank, with a relatively large width dimension on the side of the #3 cylinder and a relatively small width dimension on the side of the #1 cylinder (see FIG. 3). The plate-shaped lower deck 11 has an appropriate thickness to have the necessary rigidity. Note that the cylinder bore 16 terminates at the lower surface of the lower deck 11. That is, the cylinder wall 13 does not protrude below the lower deck 11. In the state finally assembled as an internal combustion engine, a crankcase component (for example, an oil pan) not shown is attached to the lower surface of the lower deck 11.

[0015] The main bearing portions 15 are provided at a total of four locations, namely, at both the front and rear ends in the cylinder row direction and at positions between the cylinders, in order to rotatably support a crankshaft (not shown). The main bearing portions 15 are each formed to protrude downward from the lower surface of the lower deck 11 so as to have a relatively thick plate shape of a rectangle, and each has a semi-circular bearing recess 15a at the center of its lower surface. Finally, bearing caps (not shown) are attached to these main bearing portions 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 forms a flat surface along one plane orthogonal to the cylinder axis direction, excluding the main bearing portions 15.

[0016] The cylinder wall 13 has a cylindrical shape with a substantially constant thickness (radial dimension). Also, in the illustrated example, three cylindrical cylinder walls 13 form a so-called siamese structure in which they are connected to each other at the portion between the cylinders. That is, the bore pitch is shorter than the outer diameter of the cylinder wall 13. In the illustrated example, since the main block 2 is formed of an aluminum alloy, 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 sprayed thereon.

[0017] The pedestal portion 12 has a side surface 21 that rises 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 substantially perpendicularly (in other words, along the cylinder axis direction) from the top surface 22 of the pedestal portion 12.

[0018] The columnar portions 14 are provided at a total of eight locations, namely, at both front and rear ends in the cylinder row direction and at positions between cylinders, so as to surround a cylinder row in which three cylinder walls 13 are in series. Hereinafter, when it is necessary to distinguish each of them, as shown in FIG. 4, starting from the #1 cylinder side in order, they are called the first columnar portion 14A, the second columnar portion 14B, the third columnar portion 14C, the fourth columnar portion 14D, the fifth columnar portion 14E, the sixth columnar portion 14F, the seventh columnar portion 14G, and the eighth columnar portion 14H, and when there is no need for distinction, they are collectively referred to as the columnar portion 14. Each of the columnar portions 14 is independent and separated from the cylinder wall 13. These columnar portions 14 function as bolt boss portions into which cylinder head bolts (not shown) for fixing a cylinder head (not shown) disposed on the cylinder block 1 are respectively screwed.

[0019] Six columnar portions 14 excluding the first columnar portion 14A and the second columnar portion 14B, that is, the third columnar portion 14C to the eighth columnar portion 14H, each form a simple cylindrical shape with a circular cross-section, and bolt holes 24 into which cylinder head bolts are screwed are formed at the centers of their upper end portions. Basically, the diameters of the third columnar portion 14C to the eighth columnar portion 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, so-called draft gradients are given to the surfaces of each part along the cylinder axis direction as required. Therefore, the third columnar portion 14C to the eighth columnar portion 14H, which are cylindrical, strictly speaking, have a tapered shape in which the upper end portion is slightly smaller in diameter.

[0020] Unlike the third to eighth columnar portions 14C to 14H, the first columnar portion 14A has a shape as if two parallel cylinders are joined at a part of their outer circumferential surfaces. In other words, in a plan view as shown in FIG. 5 and a cross-sectional view orthogonal to the cylinder axis direction, it has a figure-eight shape. Specifically, a main cylinder portion 14Aa having the same diameter as the third to eighth columnar portions 14C to 14H and a sub-cylinder portion 14Ab having a smaller diameter than this are integrated. The main cylinder portion 14Aa is a portion that functions as a bolt boss portion for a cylinder head bolt in the same manner as the third to eighth columnar portions 14C to 14H, and has a bolt hole 24 at the center of the upper end portion. This main cylinder portion 14Aa is provided at a position symmetric to the fourth columnar portion 14D with the cylinder center of the #1 cylinder interposed therebetween, that is, at a position where the arrangement of a total of eight cylinder head bolts is uniform. The sub-cylinder portion 14Ab is located on the diagonally outer side of the main cylinder portion 14Aa, that is, on the side opposite to the cylinder wall 13 of the #1 cylinder. An oil passage 25 along the cylinder axis direction for supplying oil pressurized by an oil pump (not shown) to the cylinder head is formed at the center of this sub-cylinder portion 14Ab. In other words, the sub-cylinder portion 14Ab corresponds to a pipe constituting the oil passage 25 having a circular cross-section. Thus, the first columnar portion 14A is one in which the main cylinder portion 14Aa serving as a bolt boss portion and the sub-cylinder portion 14Ab serving as a pipe of the oil passage 25 are connected at a part of their circumferential surfaces, and a pair of concave groove portions 14Ac remain on the outer circumferential surface between the two.

[0021] The second columnar portion 14B is similar to the first columnar portion 14A and has a shape as if two parallel cylinders are joined at a part of their outer peripheral surfaces. In other words, in a plan view as shown in FIG. 5 and a cross-sectional view orthogonal to the cylinder axis direction, it has a figure-eight shape. Specifically, a main cylindrical portion 14Ba having a smaller diameter than the third columnar portion 14C to the eighth columnar portion 14H and a sub-cylindrical portion 14Bb having a slightly smaller diameter than this are integrated. The main cylindrical portion 14Ba is a portion that functions as a bolt boss portion for the cylinder head bolts in the same manner as 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 cylindrical portion 14Ba is provided at a position symmetric to the third columnar portion 14C with the cylinder center of the #1 cylinder in between, that is, at a position where the arrangement of a total of eight cylinder head bolts is uniform. The sub-cylindrical portion 14Bb is located in front of the main cylindrical portion 14Ba and inside in the width direction, that is, adjacent to the main cylindrical portion 14Ba on an arc centered on the cylinder center of the #1 cylinder. At the center of this sub-cylindrical portion 14Bb, an oil passage 26 along the cylinder axis direction for supplying oil pressurized by an oil pump (not shown) to the cylinder head is formed in the same manner as the sub-cylindrical portion 14Ab of the first columnar portion 14A. In other words, the sub-cylindrical portion 14Bb corresponds to a pipe constituting the oil passage 26 having a circular cross-section. Thus, the second columnar portion 14B is formed by connecting the main cylindrical portion 14Ba serving as a bolt boss portion and the sub-cylindrical portion 14Bb serving as a pipe of the oil passage 26 at a part of the peripheral surface, and a pair of concave groove portions 14Bc remain on the outer peripheral surface between the two.

[0022] Further, in the illustrated example, while the other columnar portions 14 (the first columnar portion 14A, the third columnar portion 14C to the eighth columnar portion 14H) protrude from the top surface 22 of the pedestal portion 12 without being continuous with the side surface 21 of the pedestal portion 12, the lower portion of the second columnar portion 14B is configured to be integrated with the side surface 21 of the pedestal portion 12. That is, among the outer peripheral surfaces of the second columnar portion 14B having a figure-eight cross-sectional shape, the inner portion (the portion toward the cylinder wall 13) rises from the top surface 22 of the pedestal portion 12, while the outer portion (the portion on the side opposite to the cylinder wall 13) extends downward from the top surface 22 and is continuous to the lower deck 11.

[0023] The lower end portions of the oil passages 25 passing through the first columnar portion 14A and the lower end portions of the oil passages 26 passing through the second columnar portion 14B communicate with a sub-oil gallery (not shown) extending in the width direction of the main block 2 formed near the front end portion of the lower deck 11, respectively. And this sub-oil gallery along the width direction communicates with 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 the cylinder walls 13. High-pressure oil (lubricating oil) pressurized from 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 the 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 the oil passage 28 passing through the main bearing portion 15.

[0024] The pedestal portion 12 is formed so as to project outward with a substantially constant width from the outer contour of the three cylinder walls 13 arranged in series, and is formed so as to project outward with a substantially constant width from the outer contour of the columnar portions 14 excluding the second columnar portion 14B. That is, the shape of the side surface 21 of the pedestal portion 12 is determined so as to surround the outside along the outer contours of the cylinder walls 13 and the columnar portions 14. Basically, the side surface 21 is a combination of a cylindrical surface concentric with the cylinder wall 13 and a cylindrical surface concentric with the columnar portion 14.

[0025] In other words, as shown in FIG. 5, the top surface 22 exists with a substantially constant width (see reference numeral D1 in FIG. 5) around the cylinder wall 13 excluding the adjacent portion to the columnar portion 14, and the top surface 22 exists with a relatively narrow substantially constant width (see reference numeral D2 in FIG. 5) around the columnar portion 14. Around the first columnar portion 14A, the top surface 22 exists with the same width as around the other columnar portions 14 along the figure-eight cross-sectional shape of the first columnar portion 14A. Also, a top surface 22 exists with a relatively narrow width between each columnar portion 14 excluding the second columnar portion 14B and the adjacent cylinder wall 13.

[0026] Regarding the second columnar portion 14B, since both the main cylindrical portion 14Ba and the sub-cylindrical portion 14Bb have a smaller diameter than the other columnar portions 14, a top surface 22 having a width approximately the same as the width other than the adjacent portions with the other columnar portions 14 (see D1 in FIG. 5) exists between the top surface 22 and the cylinder wall 13. On the other hand, on the outside of the second columnar portion 14B, there is no top surface 22.

[0027] Furthermore, the pedestal portion 12 is provided with three oil drain hole forming portions 31 that form a square shape in plan view. The first oil drain hole forming portion 31A is located outside the third columnar portion 14C between the #1 cylinder and the #2 cylinder, and the second oil drain hole forming portion 31B is located outside the fifth columnar portion 14E between the #2 cylinder and the #3 cylinder. The third oil drain hole forming portion 31C is on the opposite side across the cylinder row from these two oil drain hole forming portions 31A and 31B, and is between the fourth columnar portion 14D and the sixth columnar portion 14F, that is, on the side of the #2 cylinder. In the central portion of these oil drain hole forming portions 31, an oil drain hole lower half portion 32 extending in the cylinder axis direction is formed respectively. As will be described later, this oil drain hole lower half portion 32 constitutes a part of the oil drain hole for returning the oil used on the cylinder head side to the crankcase by its own weight. As shown in the opening shape in FIG. 5, the oil drain hole lower half portion 32 has a substantially rectangular cross-sectional shape that is elongated in the cylinder row direction, but at the lower surface of the lower deck 11 that is the final oil outlet, as shown in FIG. 3, it is constricted into a circular hole.

[0028] As shown in FIGS. 4 and 5, the oil drain hole forming portion 31 has the same height as around the cylinder wall 13 as a part of the pedestal portion 12, and a part of the top surface 22 of the pedestal portion 12 that forms the same plane surrounds the periphery of the oil drain hole lower half portion 32.

[0029] The top surface 22 of the pedestal portion 12 is along one plane orthogonal to the cylinder axis direction, 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 drain hole 32. As will be described later, this top surface 22 is a surface that serves as a joint surface with the synthetic resin outer member 3, forms a plane orthogonal to the cylinder axis direction, and thus is a plane parallel to the lower surface of the lower deck 11.

[0030] Next, the synthetic resin outer member 3 is not a member that supports the load or reaction force associated with the combustion and explosion of the internal combustion engine. It mainly forms a water jacket through which cooling water flows between the main block 2 and constitutes an upper deck portion that serves as a joint surface with the cylinder head. It is integrally formed with 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 in which glass fibers are blended with a polyamide resin.

[0031] As shown in FIGS. 6 to 10, the outer member 3 generally has a substantially rectangular frame shape or cylindrical shape as a whole. The outer member 3 mainly includes an upper deck portion 41 that serves as a joint surface or boundary surface with the cylinder head, a water jacket forming wall 42 that surrounds the columnar portions 14 other than the cylinder wall 13 and the second columnar portion 14B of the main block 2 to form a water jacket, a joint flange portion 43 that projects inward from the lower end of the water jacket forming wall 42, a front flange portion 44 and a rear flange portion 45 that serve as the front end surface and the rear end surface of the composite cylinder block 1, an oil drain hole forming portion 46 corresponding to the oil drain hole forming portion 31 on the main block 2 side, and a lower side wall portion 47 that covers the periphery of the pedestal portion 12 on the main block 2 side. As will be described later, the outer member 3 is combined with the main block 2 by covering the main block 2 while accommodating the cylinder wall 13 of the main block 2 inside the inner circumference of the water jacket forming wall 42.

[0032] The upper deck portion 41 is continuous in a substantially rectangular frame shape at the upper end of the outer member 3, and its upper surface forms a flat surface along one plane orthogonal to the cylinder axis direction. The upper deck portion 41 includes linear left and right side edge portions 41a, 41b, a front edge portion 41c, and a rear edge portion 41d. The side edge portions 41a, 41b are connected to the upper part of the water jacket forming wall 42 located inside via several ribs 41e extending in the width direction. The upper end surface of the water jacket forming wall 42 constitutes a part of the upper deck portion 41 and is along one plane together with the side edge portions 41a, 41b, the front edge portion 41c, and the rear edge portion 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 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.

[0033] In plan view, the water jacket forming wall 42 has a shape generally following the outer contour of the cylinder wall 13 and the columnar portions 14 (excluding the second columnar portion 14B) of the main block 2, and has a wall surface substantially parallel to the cylinder axis direction. More specifically, the water jacket forming wall 42 is composed of a total of eight cylinder facing surfaces 51, three on each of the left and right sides that are relatively gently curved and face the outer peripheral surface of the cylinder wall 13 without overlapping the columnar portions 14, and two at the front and rear ends, 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 distinguish the eight cylinder facing surfaces 51 individually, they are designated as the first cylinder facing surface 51A, the second cylinder facing surface 51B... the eighth cylinder facing surface 51H in order from the front end in the clockwise direction. For the seven columnar portion facing surfaces 52, they are individually distinguished as the first columnar portion facing surface 52A, the third columnar portion facing surface 52C... the eighth columnar portion facing surface 52H according to the name of the columnar portion 14 inserted therein. The columnar portion facing surfaces 52 are each located between two adjacent cylinder facing surfaces 51 and are recessed in the form of a concave groove surface with a relatively small radius of curvature.

[0034] When combined with the main block 2, as shown in Fig. 1, the cylinder opposing surface 51 is set in such a position that an appropriate gap (in other words, a water jacket), for example, about several millimeters, is formed between it and the cylinder wall 13. On the other hand, the columnar part opposing surface 52 forms an arc surface with a diameter slightly larger than the diameter of each columnar part 14 so that a relatively small gap is formed between it and the outer peripheral surface of each columnar part 14, and is configured to be generally concentric with each columnar part 14 when combined with the main block 2. More specifically, the third columnar part opposing surface 52C to the sixth columnar part opposing surface 52F corresponding to the third columnar part 14C to the sixth columnar part 14F form cylindrical surfaces with a substantially semi-circular cross-section respectively. The seventh columnar part opposing surface 52G and the eighth columnar part opposing surface 52H corresponding to the seventh columnar part 14G and the eighth columnar part 14H are located at positions corresponding to the corner parts of the ends of the continuous water jacket, so they form cylindrical surfaces with a cross-section of about 3 / 4 of a circle larger than a semi-circle. That is, about 3 / 4 of the circumference of the seventh columnar part 14G and the eighth columnar part 14H is surrounded by the seventh columnar part opposing surface 52G and the eighth columnar part opposing surface 52H. The first columnar part opposing surface 52A corresponding to the first columnar part 14A has a cross-sectional shape along the outer shape of the figure-eight corresponding to the first columnar part 14A with a figure-eight cross-section so that a slight gap remains throughout the circumference. Thereby, as shown in Fig. 1, the first columnar part 14A fits into the first columnar part opposing surface 52A with a slight gap remaining throughout the circumference.

[0035] Regarding the second columnar portion 14B, the water jacket forming wall 42 does not have a corresponding concave groove portion (columnar portion facing surface). For the second columnar portion 14B, so as to be independent from the water jacket, on the outside of the water jacket forming wall 42 (specifically, the first cylinder facing surface 51A to the eighth cylinder facing surface 51H), a second columnar portion insertion hole 53 is formed in a pipe shape extending in the cylinder axis direction (see FIGS. 6 and 10). The second columnar portion insertion hole 53 has a cross-sectional shape along the outer shape of the "8" so that a slight gap remains all around corresponding to the second columnar portion 14B having a cross-sectional shape of "8". The second columnar portion insertion hole 53 having a cross-sectional shape along the outer shape of the "8" has an upper end opening to the upper surface of the upper deck portion 41 and extends downward therefrom. Thereby, as shown in FIGS. 1 and 2, the second columnar portion 14B fits into the second columnar portion insertion hole 53 with a slight gap remaining all around.

[0036] The joint flange portion 43 projecting inward from the lower end of the water jacket forming wall 42 is formed along a single plane orthogonal to the cylinder axis direction together with the lower end surface of the water jacket forming wall 42 and constitutes the outer member side joint surface 57. This outer member side joint surface 57 basically has a shape corresponding to the region of the top surface 22 of the pedestal portion 12 of the main block 2. That is, the joint flange portion 43 projects in a eaves shape along the contour around the three cylinder walls 13 continuously connected in a series on the top surface 22 of the pedestal portion 12, and has seven openings 54 corresponding to the seven columnar portions 14 excluding the second columnar portion 14B. The outer member side joint surface 57 is continuously configured on these lower surfaces. 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 has a substantially "8" shape similar to the first columnar portion facing surface 52A. The outer opening edge of each opening 54 is continuous in the cylinder axis direction without a step with the corresponding columnar portion facing surface 52.

[0037] Here, on the outer member side joint surface 57 including the lower surface of the water jacket constituting wall 42 and the lower surface of the joint flange portion 43, as shown in FIGS. 7, 8, and 10, for heat welding of the synthetic resin material, a welding rib 56 protruding downward in a bead shape with a certain width is formed from the outer member side joint surface 57. The welding rib 56 has a main welding rib 56a continuous over the entire circumference so as to pass outside the three cylinder walls 13 and the seven columnar portions 14 similar to the contour of the water jacket constituting wall 42, and arc-shaped welding ribs 56b for columnar portions along the inner portions (portions entering between the cylinders) of the seven openings 54, and the welding ribs 56b for columnar portions are continuous with the main welding rib 56a.

[0038] Note that FIGS. 10 and 8 show the welding rib 56 on the outer member 3 before the welding process. In the state where the outer member 3 is joined to the main block 2 through the welding process, the welding rib 56 is heated and melted, so that its height (protrusion amount) decreases and only a slight amount remains.

[0039] The oil drain 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 drain hole forming portions 31 on the main block 2 side, respectively. Each oil drain hole forming portion 46 protrudes downward in a pipe shape from the upper deck portion 41, and an upper half portion 58 of the oil drain hole extending in the cylinder axis direction is formed on the inner peripheral side. The upper half portion 58 of this oil drain hole is continuous with the lower half portion 32 of the oil drain hole on the main block 2 side to constitute an oil drain hole leading from the cylinder head to the crankcase. The upper end of the upper half portion 58 of the oil drain hole opens between the side edge portions 41a, 41b of the upper deck portion 41 and the water jacket constituting wall 42. The lower end of the upper half portion 58 of the oil drain hole opens in an elongated shape along the cylinder row direction in the same plane as the lower surfaces of the joint flange portion 43 and the water jacket constituting wall 42, as shown in FIGS. 7 and 10. That is, the lower end surface of the oil drain hole forming portion 46 constitutes a part of the outer member side joint surface 57, and the lower end of the upper half portion 58 of the oil drain hole opens in the outer member side joint surface 57. Then, welding ribs 56 (welding ribs 56c for oil drain holes) similar to those described above are formed on the outer member side joint surface 57 so as to surround the periphery of each upper half portion 58 of the oil drain hole.

[0040] The front flange portion 44 has an upper end continuous with the front edge portion 41c of the upper deck portion 41 and constitutes a flange surface 44a (see FIG. 6) with relatively high rigidity. Similarly, the rear flange portion 45 has an upper end continuous with the rear edge portion 41d of the upper deck portion 41 and constitutes a flange surface 45a (see FIG. 7) with relatively high rigidity. The flange surfaces 44a and 45a are along a plane orthogonal to the cylinder row direction.

[0041] The lower side wall portion 47 extends downward along the cylinder axis direction from a position on the outer peripheral side of the outer member side joint surface 57 so as to cover the periphery of the pedestal portion 12 on the main block 2 side. The lower end of the lower side wall portion 47 is configured to reach near the upper surface of the upper deck portion 41 when combined with the main block 2. Further, at the location of the oil drain hole forming portion 46, the lower side wall portion 47 is notched to avoid interference with the oil drain hole forming portion 31 on the main block 2 side.

[0042] In addition, a cooling water inlet 59 (see FIG. 6) leading from the outer surface of the outer member 3 to the water jacket is provided in the eighth cylinder facing surface 51H on the side of the #1 cylinder.

[0043] Next, the joining of the main block 2 and the outer member 3 and the composite cylinder block 1 finally formed by this joining will be described.

[0044] As described above, the metal main block 2 and the synthetic resin outer member 3 are individually manufactured 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 pedestal portion 12 and the outer member side joining surface 57. In the joining process, a heater for heating is disposed on the lower surface of the lower deck 11 of the metal main block 2, and the pedestal portion 12 is heated from below while the main block 2 and the outer member 3 are separated. The heater has, for example, a plate-like configuration with four rectangular openings through which the main bearing portions 15 respectively pass, and is provided in a range at least covering the projection surface of the pedestal portion 12 and is arranged to be substantially in close contact with the lower surface of the lower deck 11. By heating using this heater, when the temperature near the top surface 22 of the pedestal portion 12, which becomes the joining surface on the main block 2 side, rises to an appropriate temperature (for example, about 200 to 300 ° C) at which the welding ribs 56 of the synthetic resin outer member 3 can be melted and softened, the outer member side joining surface 57 is brought into close contact with the top surface 22 of the pedestal portion 12, and the outer member 3 is pressed toward the main block 2. Thereby, the welding ribs 56 are melted and the main block 2 and the outer member 3 are integrally joined. Therefore, the welding ribs 56 become a substantial sealing line between the two. In addition, in order to increase the joining force, if necessary, the top surface 22 of the pedestal portion 12 that becomes the joining surface may be appropriately primed in advance.

[0045] In the integrally joined state, 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 pedestal portion 12 provided so as to surround the periphery of the cylinder wall 13 and the outer member side joining surface 57. That is, in the welding ribs 56 serving as the sealing line shown in FIG. 10, the water jacket is sealed. In addition, in the state where the welding ribs 56 are 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 substantially on the same plane. In consideration of the fact 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 made slightly lower than the upper end surface of the cylinder wall 13 of the main block 2.

[0046] Of the other seven columnar portions 14 excluding the second columnar portion 14B, all are within the water jacket, and the cooling water surrounds the outer peripheral surface of the columnar portion 14. The sealing line composed of the welding rib 56 passes outside the seven columnar portions 14, that is, outside the opening 54 (on the side of the water jacket forming wall 42), and seals the water jacket in a form including the seven columnar portions 14. Therefore, for example, as shown in FIG. 11, there is a relatively narrow water jacket between the outer peripheral surface of the columnar portion 14 and the water jacket forming wall 42 (the columnar portion facing surface 52).

[0047] In contrast, the second columnar portion 14B is housed in the second columnar portion insertion hole 53 of the outer member 3 and is isolated from the water jacket. That is, the second columnar portion 14B is surrounded by the wall around the second columnar portion insertion hole 53 made of synthetic resin and does not come into contact with the cooling water. There is a slight gap serving as an air layer between the inner wall surface of the second columnar portion insertion hole 53 and the outer peripheral surface of the second columnar portion 14B.

[0048] The cylinder head (not shown) is disposed on the upper surface of the upper deck portion 41 and is fixed via cylinder head bolts. The cylinder head bolts are respectively screwed into the bolt holes 24 of the columnar portions 14. The columnar portions 14 serving as bolt boss portions are all continuously in a straight line along the cylinder axis direction up to the pedestal portion 12, and linearly transmit the load along the bolt axis direction to the pedestal portion 12. And the pedestal portion 12 is thick and firmly configured, and the pedestal portion 12 reliably supports the load acting from the cylinder head. Similarly, the main bearing portion 15 is integrated with the firm pedestal portion 12 and can reliably support the crankshaft.

[0049] Further, as shown in FIGS. 1 and 11, the oil drain hole forming portion 31 of the main block 2 and the oil drain hole forming portion 46 of the outer member 3 are joined in a butted manner with each other. Similar to the water jacket, the welding rib 56(56c) provided on the outer member 3 side is melted and softened and joined to the joint surface (top surface 22) on the main block 2 side. Thereby, the lower half portion 32 of the oil drain hole and the upper half portion 58 of the oil drain hole are continuous as a single passage, and the oil drain hole is formed. The upper end of the oil drain hole is further connected to the oil drain hole on the cylinder head side.

[0050] Thus, the composite cylinder block 1 of the above embodiment is configured such that the metal main block 2 that receives loads and reaction forces has a minimum volume, and many parts such as the water jacket constituent wall 42 are made of synthetic resin as the outer member 3, so that a significant weight reduction can be achieved.

[0051] Next, the main part of the present invention will be described. The above-described composite cylinder block 1 has a metal main block 2 and a synthetic resin outer member 3 manufactured individually, and the two are integrally joined by heat welding such as a kind of hot plate welding, so the manufacturing process is simple and it can be manufactured at low cost. As described above, the composite cylinder block 1 of the above embodiment is provided with an oil drain hole extending from the cylinder head to the crankcase. The upper half of this oil drain hole is formed inside the synthetic resin material of the outer member 3 as the upper half 58 of the oil drain hole, and the lower half is formed inside the metal material of the main block 2 as the lower half 32 of the oil drain hole. That is, since the oil flowing through the oil drain hole has already been used on the cylinder head side and the pressure has decreased, a high oil pressure does not act on the oil drain hole. That is, high pressure resistance is not required, and it is possible to provide a part of the oil drain hole on the side of the synthetic resin outer member 3. Further, since a high oil pressure does not act, the requirement for the sealing property at the joint surface (welding surface) between the main block 2 and the outer member 3 surrounding the oil drain hole is not severe. By configuring the upper half of the oil drain hole on the side of the lightweight outer member 3 in this way, the overall weight of the composite cylinder block 1 can be reduced compared to the case where the entire oil drain hole is formed inside a metal member. Note that the terms "upper half" and "lower half" do not mean having a length of 1 / 2 respectively.

[0052] On the other hand, for the oil passages 25, 26 through which high-pressure oil flows, they are formed inside the metal material of the metal main block 2, specifically, through the inside of the columnar portions 14 (the first columnar portion 14A and the second columnar portion 14B) that rise from the pedestal portion 12 and reach the upper surface of the upper deck portion 41. Therefore, high pressure resistance can be ensured for the entire passage, and problems such as sealing with respect to the joint surface at the intermediate height position do not occur. By providing the two oil passages 25, 26 substantially in parallel as flow paths, the passage cross-sectional area of each of the oil passages 25, 26 can be made smaller compared to the amount of oil required on the cylinder head side. As described above, it is possible to form the oil passages 25, 26 together with the bolt holes 24 in the first columnar portion 14A and the second columnar portion 14B.

[0053] In addition, the cylinder head bolts for fixing the cylinder head are screwed into the respective bolt holes 24, with the columnar portions 14 rising from the pedestal portion 12 of the metal main block 2 and reaching the upper surface of the upper deck portion 41 serving as bolt boss portions. Therefore, sufficient strength and rigidity can be ensured against combustion, explosion, etc.

[0054] The columnar portions 14 form columns with a relatively small cross-sectional area, including the first columnar portion 14A and the second columnar portion 14B having oil passages 25 and 26, so the weight increase due to this is relatively small. Further, the oil drain hole forming portion 31 on the main block 2 side is provided in a form that projects relatively small to the side of the pedestal portion 12 generally corresponding to the contour of the cylinder wall 13, so the weight increase associated with the formation of this oil drain hole forming portion 31 is also minimized.

[0055] Furthermore, in the above embodiment, the top surface 22 of the pedestal portion 12 of the metal main block 2 and the outer member side joint surface 57 of the synthetic resin outer member 3 are joined to each other to form a welded surface. This welded surface (top surface 22 and outer member side joint surface 57) includes the welded surface around the oil drain hole (the portion along the welded rib 56c for the oil drain hole) and the welded surface surrounding the water jacket (the portion along the main welded rib 56a and the welded rib 56b for the columnar portion), and the entire surface is on one plane perpendicular to the cylinder axis direction. Therefore, when the outer member 3 is pressed toward the main block 2 in the welding process, the load acts evenly around the oil drain hole and around the water jacket. As a result, uniform welding quality can be obtained in each part. Here, although not shown, as another preferred embodiment, the welded surface around the oil drain hole and the welded surface around the water jacket may be along planes perpendicular to the cylinder axis direction, respectively, while being formed at different height positions from each other. In particular, it is preferable to arrange the welded surface around the oil drain hole below the welded surface around the water jacket (that is, the top surface 22 around the cylinder wall 13) in the cylinder axis direction. By configuring each welded surface in a stepped shape in this way, the proportion occupied by the upper half 58 of the oil drain hole formed by the lightweight synthetic resin outer member 3 increases, which is advantageous in terms of reducing the overall weight of the composite cylinder block 1.

[0056] As described above, one embodiment of the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various modifications are possible. For example, the specific shape, position, etc. of the oil drain hole forming portions 31 and 46 can be appropriately changed.

Explanation of Reference Numerals

[0057] 1... Composite cylinder block 2... Main block 3... Outer member 11... Lower deck 12... Pedestal portion 13... Cylinder wall 14... Columnar portion 15... Main bearing portion 24... Bolt hole 25, 26… Oil passage 31… Oil drain hole forming part 32… Lower half of the oil drain hole 41… Upper deck part 42… Water jacket forming wall 46… Oil drain hole forming part 58… Upper half of the oil drain hole

Claims

1. A composite cylinder block comprising a metallic 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 form a water jacket between the cylinder wall and having an upper deck portion on which a cylinder head is disposed on an upper surface, and the two being integrally joined, wherein an upper half of an oil drain hole extending from the cylinder head to a crankcase below the main block is formed inside a synthetic resin material of the outer member, and a lower half is formed inside a metallic material of the main block, and a periphery of the oil drain hole is surrounded by a joint surface.

2. An oil passage for supplying oil pressurized by an oil pump from a lower portion of the composite cylinder block to the cylinder head is provided, and the entire oil passage is formed inside a metallic material of the main block. The composite cylinder block according to claim 1.

3. The main block includes a columnar portion rising up to reach an upper surface of the upper deck portion, and the oil passage is formed through the inside of the columnar portion. The composite cylinder block according to claim 2.

4. The main block includes a plurality of columnar portions rising up to reach an upper surface of the upper deck portion corresponding to cylinder head bolts for fixing a cylinder head disposed on the upper surface of the upper deck portion, and bolt holes into which the cylinder head bolts are screwed are provided in each columnar portion. The composite cylinder block according to claim 1.

5. The outer member is heat-welded to the main block by heating the main block, and an entire welding surface between the main block and the outer member including a periphery of the oil drain hole is on one plane orthogonal to a cylinder axis direction. The composite cylinder block according to any one of claims 1 to 4.

6. The outer member is heat-welded to the main block by heating the main block, A second welding surface provided around the oil drain hole and a first welding surface provided around the water jacket are each along a plane orthogonal to the cylinder axis direction, The composite cylinder block according to any one of claims 1 to 4, wherein the second welding surface is located below the first welding surface in the cylinder axis direction.

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